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	$82.45	12.211%	$92.518	$92.52	$92.50	$92.50
Purchase #2	$187.35	4.705%	$196.1648	$196.16	$196.15	$196.20
Purchase #3	$194.61	7.684%	$209.5638	$209.56	$209.55	$209.60
Purchase #4	$32.40	3.180%	$33.4303	$33.43	$33.45	$33.40
Purchase #5	$7.58	5.143%	$7.9698	$7.97	$7.95	$8.00
Purchase #6	$120.25	8.715%	$130.7298	$130.73	$130.75	$130.70
Purchase #7	$85.36	5.145%	$89.7518	$89.75	$89.75	$89.80
7 purchase totals =	$710.00		$760.1283	$760.12	$760.10	$760.20