Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$66.92	9.359%	$73.183	$73.18	$73.20	$73.20
Purchase #2	$103.36	7.676%	$111.2939	$111.29	$111.30	$111.30
Purchase #3	$102.89	7.624%	$110.7343	$110.73	$110.75	$110.70
Purchase #4	$30.85	8.626%	$33.5111	$33.51	$33.50	$33.50
Purchase #5	$87.44	3.571%	$90.5625	$90.56	$90.55	$90.60
Purchase #6	$104.82	8.707%	$113.9467	$113.95	$113.95	$113.90
Purchase #7	$247.50	6.200%	$262.845	$262.85	$262.85	$262.80
7 purchase totals =	$743.78		$796.0765	$796.07	$796.10	$796.00