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	$84.97	6.427%	$90.431	$90.43	$90.45	$90.40
Purchase #2	$38.64	3.646%	$40.0488	$40.05	$40.05	$40.00
Purchase #3	$168.50	10.345%	$185.9313	$185.93	$185.95	$185.90
Purchase #4	$7.67	10.202%	$8.4525	$8.45	$8.45	$8.50
Purchase #5	$10.27	10.620%	$11.3607	$11.36	$11.35	$11.40
Purchase #6	$33.32	11.563%	$37.1728	$37.17	$37.15	$37.20
Purchase #7	$195.81	13.556%	$222.354	$222.35	$222.35	$222.40
7 purchase totals =	$539.18		$595.7511	$595.74	$595.75	$595.80