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	$11.45	6.195%	$12.1593	$12.16	$12.15	$12.20
Purchase #2	$217.91	7.367%	$233.9634	$233.96	$233.95	$234.00
Purchase #3	$80.54	13.864%	$91.7061	$91.71	$91.70	$91.70
Purchase #4	$126.44	10.507%	$139.7251	$139.73	$139.75	$139.70
Purchase #5	$103.32	12.486%	$116.2205	$116.22	$116.20	$116.20
Purchase #6	$103.45	11.309%	$115.1492	$115.15	$115.15	$115.10
Purchase #7	$98.51	13.213%	$111.5261	$111.53	$111.55	$111.50
7 purchase totals =	$741.62		$820.4497	$820.46	$820.45	$820.40