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	$93.41	13.326%	$105.8578	$105.86	$105.85	$105.90
Purchase #2	$37.27	11.430%	$41.53	$41.53	$41.55	$41.50
Purchase #3	$87.32	8.125%	$94.4148	$94.41	$94.40	$94.40
Purchase #4	$60.97	5.272%	$64.1843	$64.18	$64.20	$64.20
Purchase #5	$61.50	9.678%	$67.452	$67.45	$67.45	$67.50
Purchase #6	$32.78	3.211%	$33.8326	$33.83	$33.85	$33.80
Purchase #7	$12.25	4.200%	$12.7645	$12.76	$12.75	$12.80
7 purchase totals =	$385.50		$420.0360	$420.02	$420.05	$420.10