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	$98.93	13.584%	$112.3687	$112.37	$112.35	$112.40
Purchase #2	$244.81	11.786%	$273.6633	$273.66	$273.65	$273.70
Purchase #3	$91.42	10.117%	$100.669	$100.67	$100.65	$100.70
Purchase #4	$151.48	6.231%	$160.9187	$160.92	$160.90	$160.90
Purchase #5	$40.60	10.159%	$44.7246	$44.72	$44.70	$44.70
Purchase #6	$57.34	9.248%	$62.6428	$62.64	$62.65	$62.60
Purchase #7	$133.82	11.598%	$149.3404	$149.34	$149.35	$149.30
7 purchase totals =	$818.40		$904.3275	$904.32	$904.25	$904.30