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	$203.60	8.494%	$220.8938	$220.89	$220.90	$220.90
Purchase #2	$131.26	6.561%	$139.872	$139.87	$139.85	$139.90
Purchase #3	$109.67	5.406%	$115.5988	$115.60	$115.60	$115.60
Purchase #4	$25.25	4.588%	$26.4085	$26.41	$26.40	$26.40
Purchase #5	$54.30	13.515%	$61.6386	$61.64	$61.65	$61.60
Purchase #6	$41.86	8.576%	$45.4499	$45.45	$45.45	$45.40
Purchase #7	$81.62	10.624%	$90.2913	$90.29	$90.30	$90.30
7 purchase totals =	$647.56		$700.1529	$700.15	$700.15	$700.10