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	$48.33	13.209%	$54.7139	$54.71	$54.70	$54.70
Purchase #2	$12.57	4.330%	$13.1143	$13.11	$13.10	$13.10
Purchase #3	$133.93	10.777%	$148.3636	$148.36	$148.35	$148.40
Purchase #4	$120.48	8.345%	$130.5341	$130.53	$130.55	$130.50
Purchase #5	$198.86	9.625%	$218.0003	$218.00	$218.00	$218.00
Purchase #6	$144.29	13.818%	$164.228	$164.23	$164.25	$164.20
Purchase #7	$79.43	12.760%	$89.5653	$89.57	$89.55	$89.60
7 purchase totals =	$737.89		$818.5195	$818.51	$818.50	$818.50