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	$49.77	4.688%	$52.1032	$52.10	$52.10	$52.10
Purchase #2	$219.45	11.250%	$244.1381	$244.14	$244.15	$244.10
Purchase #3	$39.63	11.441%	$44.1641	$44.16	$44.15	$44.20
Purchase #4	$127.90	8.849%	$139.2179	$139.22	$139.20	$139.20
Purchase #5	$142.57	12.396%	$160.243	$160.24	$160.25	$160.20
Purchase #6	$99.85	5.378%	$105.2199	$105.22	$105.20	$105.20
Purchase #7	$115.86	12.871%	$130.7723	$130.77	$130.75	$130.80
7 purchase totals =	$795.03		$875.8585	$875.85	$875.80	$875.80