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	$138.34	5.831%	$146.4066	$146.41	$146.40	$146.40
Purchase #2	$132.70	11.526%	$147.995	$148.00	$148.00	$148.00
Purchase #3	$89.72	7.702%	$96.6302	$96.63	$96.65	$96.60
Purchase #4	$141.83	9.652%	$155.5194	$155.52	$155.50	$155.50
Purchase #5	$51.98	12.797%	$58.6319	$58.63	$58.65	$58.60
Purchase #6	$149.87	10.284%	$165.2826	$165.28	$165.30	$165.30
Purchase #7	$158.83	8.447%	$172.2464	$172.25	$172.25	$172.20
7 purchase totals =	$863.27		$942.7121	$942.72	$942.75	$942.60