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	$48.43	13.367%	$54.9036	$54.90	$54.90	$54.90
Purchase #2	$176.76	8.174%	$191.2084	$191.21	$191.20	$191.20
Purchase #3	$82.79	12.391%	$93.0485	$93.05	$93.05	$93.00
Purchase #4	$93.92	6.802%	$100.3084	$100.31	$100.30	$100.30
Purchase #5	$6.55	9.774%	$7.1902	$7.19	$7.20	$7.20
Purchase #6	$28.66	10.611%	$31.7011	$31.70	$31.70	$31.70
Purchase #7	$94.79	4.578%	$99.1295	$99.13	$99.15	$99.10
7 purchase totals =	$531.90		$577.4897	$577.49	$577.50	$577.40