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	$72.32	6.157%	$76.7727	$76.77	$76.75	$76.80
Purchase #2	$52.84	13.243%	$59.8376	$59.84	$59.85	$59.80
Purchase #3	$71.60	10.867%	$79.3808	$79.38	$79.40	$79.40
Purchase #4	$184.85	5.344%	$194.7284	$194.73	$194.75	$194.70
Purchase #5	$16.41	4.604%	$17.1655	$17.17	$17.15	$17.20
Purchase #6	$82.54	5.252%	$86.875	$86.88	$86.90	$86.90
Purchase #7	$16.89	7.241%	$18.113	$18.11	$18.10	$18.10
7 purchase totals =	$497.45		$532.8730	$532.88	$532.90	$532.90