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	$11.85	9.130%	$12.9319	$12.93	$12.95	$12.90
Purchase #2	$48.62	11.519%	$54.2205	$54.22	$54.20	$54.20
Purchase #3	$249.76	10.307%	$275.5028	$275.50	$275.50	$275.50
Purchase #4	$148.30	12.507%	$166.8479	$166.85	$166.85	$166.80
Purchase #5	$46.47	4.190%	$48.4171	$48.42	$48.40	$48.40
Purchase #6	$100.97	9.215%	$110.2744	$110.27	$110.25	$110.30
Purchase #7	$161.85	11.301%	$180.1407	$180.14	$180.15	$180.10
7 purchase totals =	$767.82		$848.3353	$848.33	$848.30	$848.20