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	$53.25	4.298%	$55.5387	$55.54	$55.55	$55.50
Purchase #2	$125.25	9.796%	$137.5195	$137.52	$137.50	$137.50
Purchase #3	$143.63	3.641%	$148.8596	$148.86	$148.85	$148.90
Purchase #4	$66.41	8.696%	$72.185	$72.19	$72.20	$72.20
Purchase #5	$134.72	10.112%	$148.3429	$148.34	$148.35	$148.30
Purchase #6	$16.83	13.499%	$19.1019	$19.10	$19.10	$19.10
Purchase #7	$106.34	4.350%	$110.9658	$110.97	$110.95	$111.00
7 purchase totals =	$646.43		$692.5134	$692.52	$692.50	$692.50