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	$29.94	10.724%	$33.1508	$33.15	$33.15	$33.20
Purchase #2	$110.98	3.345%	$114.6923	$114.69	$114.70	$114.70
Purchase #3	$95.48	4.563%	$99.8368	$99.84	$99.85	$99.80
Purchase #4	$200.59	3.106%	$206.8203	$206.82	$206.80	$206.80
Purchase #5	$36.25	10.672%	$40.1186	$40.12	$40.10	$40.10
Purchase #6	$219.85	11.362%	$244.8294	$244.83	$244.85	$244.80
Purchase #7	$203.53	13.189%	$230.3736	$230.37	$230.35	$230.40
7 purchase totals =	$896.62		$969.8218	$969.82	$969.80	$969.80