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	$134.45	12.203%	$150.8569	$150.86	$150.85	$150.90
Purchase #2	$220.58	8.178%	$238.619	$238.62	$238.60	$238.60
Purchase #3	$70.42	12.746%	$79.3957	$79.40	$79.40	$79.40
Purchase #4	$197.59	13.292%	$223.8537	$223.85	$223.85	$223.90
Purchase #5	$27.43	11.253%	$30.5167	$30.52	$30.50	$30.50
Purchase #6	$85.72	3.669%	$88.8651	$88.87	$88.85	$88.90
Purchase #7	$65.53	3.266%	$67.6702	$67.67	$67.65	$67.70
7 purchase totals =	$801.72		$879.7773	$879.79	$879.70	$879.90