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	$166.48	13.414%	$188.8116	$188.81	$188.80	$188.80
Purchase #2	$225.98	10.495%	$249.6966	$249.70	$249.70	$249.70
Purchase #3	$161.91	7.165%	$173.5109	$173.51	$173.50	$173.50
Purchase #4	$32.43	6.413%	$34.5097	$34.51	$34.50	$34.50
Purchase #5	$213.71	5.871%	$226.2569	$226.26	$226.25	$226.30
Purchase #6	$131.93	10.122%	$145.284	$145.28	$145.30	$145.30
Purchase #7	$53.51	11.709%	$59.7755	$59.78	$59.80	$59.80
7 purchase totals =	$985.95		$1,077.8452	$1,077.85	$1,077.85	$1,077.90