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	$75.74	12.367%	$85.1068	$85.11	$85.10	$85.10
Purchase #2	$83.90	6.474%	$89.3317	$89.33	$89.35	$89.30
Purchase #3	$143.98	10.762%	$159.4751	$159.48	$159.50	$159.50
Purchase #4	$227.97	13.821%	$259.4777	$259.48	$259.50	$259.50
Purchase #5	$66.38	12.184%	$74.4677	$74.47	$74.45	$74.50
Purchase #6	$245.44	7.772%	$264.5156	$264.52	$264.50	$264.50
Purchase #7	$208.60	7.650%	$224.5579	$224.56	$224.55	$224.60
7 purchase totals =	$1,052.01		$1,156.9325	$1,156.95	$1,156.95	$1,157.00