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	$53.76	10.637%	$59.4785	$59.48	$59.50	$59.50
Purchase #2	$30.70	8.513%	$33.3135	$33.31	$33.30	$33.30
Purchase #3	$138.73	10.461%	$153.2425	$153.24	$153.25	$153.20
Purchase #4	$91.90	13.430%	$104.2422	$104.24	$104.25	$104.20
Purchase #5	$140.25	8.131%	$151.6537	$151.65	$151.65	$151.70
Purchase #6	$231.89	7.697%	$249.7386	$249.74	$249.75	$249.70
Purchase #7	$211.26	10.700%	$233.8648	$233.86	$233.85	$233.90
7 purchase totals =	$898.49		$985.5338	$985.52	$985.55	$985.50