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	$140.97	13.749%	$160.352	$160.35	$160.35	$160.40
Purchase #2	$204.98	9.215%	$223.8689	$223.87	$223.85	$223.90
Purchase #3	$37.84	12.103%	$42.4198	$42.42	$42.40	$42.40
Purchase #4	$21.54	8.164%	$23.2985	$23.30	$23.30	$23.30
Purchase #5	$59.25	5.236%	$62.3523	$62.35	$62.35	$62.40
Purchase #6	$36.58	13.802%	$41.6288	$41.63	$41.65	$41.60
Purchase #7	$28.45	11.771%	$31.7988	$31.80	$31.80	$31.80
7 purchase totals =	$529.61		$585.7191	$585.72	$585.70	$585.80