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	$7.96	7.258%	$8.5377	$8.54	$8.55	$8.50
Purchase #2	$175.38	7.666%	$188.8246	$188.82	$188.80	$188.80
Purchase #3	$149.90	6.644%	$159.8594	$159.86	$159.85	$159.90
Purchase #4	$39.97	7.309%	$42.8914	$42.89	$42.90	$42.90
Purchase #5	$90.89	8.801%	$98.8892	$98.89	$98.90	$98.90
Purchase #6	$53.63	10.396%	$59.2054	$59.21	$59.20	$59.20
Purchase #7	$14.95	4.245%	$15.5846	$15.58	$15.60	$15.60
7 purchase totals =	$532.68		$573.7923	$573.79	$573.80	$573.80