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	$68.25	5.753%	$72.1764	$72.18	$72.20	$72.20
Purchase #2	$90.40	9.533%	$99.0178	$99.02	$99.00	$99.00
Purchase #3	$11.42	11.352%	$12.7164	$12.72	$12.70	$12.70
Purchase #4	$138.79	8.432%	$150.4928	$150.49	$150.50	$150.50
Purchase #5	$158.65	7.688%	$170.847	$170.85	$170.85	$170.80
Purchase #6	$75.61	9.429%	$82.7393	$82.74	$82.75	$82.70
Purchase #7	$58.99	13.488%	$66.9466	$66.95	$66.95	$66.90
7 purchase totals =	$602.11		$654.9363	$654.95	$654.95	$654.80