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	$131.60	13.343%	$149.1594	$149.16	$149.15	$149.20
Purchase #2	$244.83	12.657%	$275.8181	$275.82	$275.80	$275.80
Purchase #3	$158.78	7.811%	$171.1823	$171.18	$171.20	$171.20
Purchase #4	$85.67	12.468%	$96.3513	$96.35	$96.35	$96.40
Purchase #5	$79.90	4.157%	$83.2214	$83.22	$83.20	$83.20
Purchase #6	$59.62	3.276%	$61.5732	$61.57	$61.55	$61.60
Purchase #7	$97.96	7.203%	$105.0161	$105.02	$105.00	$105.00
7 purchase totals =	$858.36		$942.3218	$942.32	$942.25	$942.40