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	$37.39	10.486%	$41.3107	$41.31	$41.30	$41.30
Purchase #2	$198.49	8.609%	$215.578	$215.58	$215.60	$215.60
Purchase #3	$83.63	8.290%	$90.5629	$90.56	$90.55	$90.60
Purchase #4	$69.27	5.198%	$72.8707	$72.87	$72.85	$72.90
Purchase #5	$244.70	7.688%	$263.5125	$263.51	$263.50	$263.50
Purchase #6	$228.98	11.727%	$255.8325	$255.83	$255.85	$255.80
Purchase #7	$97.90	8.699%	$106.4163	$106.42	$106.40	$106.40
7 purchase totals =	$960.36		$1,046.0836	$1,046.08	$1,046.05	$1,046.10