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	$6.59	6.258%	$7.0024	$7.00	$7.00	$7.00
Purchase #2	$83.87	7.674%	$90.3062	$90.31	$90.30	$90.30
Purchase #3	$93.28	3.388%	$96.4403	$96.44	$96.45	$96.40
Purchase #4	$39.79	13.359%	$45.1055	$45.11	$45.10	$45.10
Purchase #5	$63.52	12.821%	$71.6639	$71.66	$71.65	$71.70
Purchase #6	$140.54	7.527%	$151.1184	$151.12	$151.10	$151.10
Purchase #7	$155.98	9.526%	$170.8387	$170.84	$170.85	$170.80
7 purchase totals =	$583.57		$632.4754	$632.48	$632.45	$632.40