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	$39.93	3.851%	$41.4677	$41.47	$41.45	$41.50
Purchase #2	$144.63	7.480%	$155.4483	$155.45	$155.45	$155.40
Purchase #3	$53.98	10.684%	$59.7472	$59.75	$59.75	$59.70
Purchase #4	$40.45	11.795%	$45.2211	$45.22	$45.20	$45.20
Purchase #5	$198.89	6.224%	$211.2689	$211.27	$211.25	$211.30
Purchase #6	$231.39	7.104%	$247.8279	$247.83	$247.85	$247.80
Purchase #7	$214.79	6.120%	$227.9351	$227.94	$227.95	$227.90
7 purchase totals =	$924.06		$988.9162	$988.93	$988.90	$988.80