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	$78.92	4.522%	$82.4888	$82.49	$82.50	$82.50
Purchase #2	$48.27	4.362%	$50.3755	$50.38	$50.40	$50.40
Purchase #3	$18.48	8.442%	$20.0401	$20.04	$20.05	$20.00
Purchase #4	$115.30	11.117%	$128.1179	$128.12	$128.10	$128.10
Purchase #5	$41.41	4.858%	$43.4217	$43.42	$43.40	$43.40
Purchase #6	$173.70	9.340%	$189.9236	$189.92	$189.90	$189.90
Purchase #7	$6.62	13.239%	$7.4964	$7.50	$7.50	$7.50
7 purchase totals =	$482.70		$521.8640	$521.87	$521.85	$521.80