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	$108.99	8.673%	$118.4427	$118.44	$118.45	$118.40
Purchase #2	$53.39	11.682%	$59.627	$59.63	$59.65	$59.60
Purchase #3	$217.89	13.771%	$247.8956	$247.90	$247.90	$247.90
Purchase #4	$118.38	8.212%	$128.1014	$128.10	$128.10	$128.10
Purchase #5	$57.62	7.190%	$61.7629	$61.76	$61.75	$61.80
Purchase #6	$67.85	9.359%	$74.2001	$74.20	$74.20	$74.20
Purchase #7	$240.54	4.562%	$251.5134	$251.51	$251.50	$251.50
7 purchase totals =	$864.66		$941.5431	$941.54	$941.55	$941.50