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	$45.71	9.722%	$50.1539	$50.15	$50.15	$50.20
Purchase #2	$42.99	4.781%	$45.0454	$45.05	$45.05	$45.00
Purchase #3	$134.90	4.661%	$141.1877	$141.19	$141.20	$141.20
Purchase #4	$25.72	9.482%	$28.1588	$28.16	$28.15	$28.20
Purchase #5	$88.80	11.867%	$99.3379	$99.34	$99.35	$99.30
Purchase #6	$101.61	6.800%	$108.5195	$108.52	$108.50	$108.50
Purchase #7	$92.80	3.743%	$96.2735	$96.27	$96.25	$96.30
7 purchase totals =	$532.53		$568.6767	$568.68	$568.65	$568.70