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	$34.88	13.351%	$39.5368	$39.54	$39.55	$39.50
Purchase #2	$56.44	9.477%	$61.7888	$61.79	$61.80	$61.80
Purchase #3	$233.46	9.358%	$255.3072	$255.31	$255.30	$255.30
Purchase #4	$222.61	8.357%	$241.2135	$241.21	$241.20	$241.20
Purchase #5	$57.84	9.143%	$63.1283	$63.13	$63.15	$63.10
Purchase #6	$220.95	5.784%	$233.7297	$233.73	$233.75	$233.70
Purchase #7	$221.40	10.444%	$244.523	$244.52	$244.50	$244.50
7 purchase totals =	$1,047.58		$1,139.2273	$1,139.23	$1,139.25	$1,139.10