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	$65.48	12.372%	$73.5812	$73.58	$73.60	$73.60
Purchase #2	$139.84	11.411%	$155.7971	$155.80	$155.80	$155.80
Purchase #3	$96.37	12.617%	$108.529	$108.53	$108.55	$108.50
Purchase #4	$55.78	5.226%	$58.6951	$58.70	$58.70	$58.70
Purchase #5	$160.58	5.749%	$169.8117	$169.81	$169.80	$169.80
Purchase #6	$59.57	12.672%	$67.1187	$67.12	$67.10	$67.10
Purchase #7	$30.88	9.188%	$33.7173	$33.72	$33.70	$33.70
7 purchase totals =	$608.50		$667.2501	$667.26	$667.25	$667.20