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	$61.97	5.171%	$65.1745	$65.17	$65.15	$65.20
Purchase #2	$202.48	10.385%	$223.5075	$223.51	$223.50	$223.50
Purchase #3	$39.42	12.703%	$44.4275	$44.43	$44.45	$44.40
Purchase #4	$86.38	6.482%	$91.9792	$91.98	$92.00	$92.00
Purchase #5	$102.34	13.779%	$116.4414	$116.44	$116.45	$116.40
Purchase #6	$13.95	8.362%	$15.1165	$15.12	$15.10	$15.10
Purchase #7	$11.77	6.266%	$12.5075	$12.51	$12.50	$12.50
7 purchase totals =	$518.31		$569.1541	$569.16	$569.15	$569.10