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	$36.64	3.801%	$38.0327	$38.03	$38.05	$38.00
Purchase #2	$104.73	11.634%	$116.9143	$116.91	$116.90	$116.90
Purchase #3	$172.61	13.218%	$195.4256	$195.43	$195.45	$195.40
Purchase #4	$56.81	7.851%	$61.2702	$61.27	$61.25	$61.30
Purchase #5	$12.38	9.433%	$13.5478	$13.55	$13.55	$13.50
Purchase #6	$171.82	10.562%	$189.9676	$189.97	$189.95	$190.00
Purchase #7	$242.56	5.610%	$256.1676	$256.17	$256.15	$256.20
7 purchase totals =	$797.55		$871.3258	$871.33	$871.30	$871.30