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	$84.68	7.134%	$90.7211	$90.72	$90.70	$90.70
Purchase #2	$39.60	4.507%	$41.3848	$41.38	$41.40	$41.40
Purchase #3	$227.30	7.621%	$244.6225	$244.62	$244.60	$244.60
Purchase #4	$238.72	4.548%	$249.577	$249.58	$249.60	$249.60
Purchase #5	$205.49	5.281%	$216.3419	$216.34	$216.35	$216.30
Purchase #6	$41.54	4.288%	$43.3212	$43.32	$43.30	$43.30
Purchase #7	$230.29	11.470%	$256.7043	$256.70	$256.70	$256.70
7 purchase totals =	$1,067.62		$1,142.6728	$1,142.66	$1,142.65	$1,142.60