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	$40.27	13.738%	$45.8023	$45.80	$45.80	$45.80
Purchase #2	$89.27	13.494%	$101.3161	$101.32	$101.30	$101.30
Purchase #3	$186.85	4.657%	$195.5516	$195.55	$195.55	$195.60
Purchase #4	$221.47	9.800%	$243.1741	$243.17	$243.15	$243.20
Purchase #5	$37.95	11.398%	$42.2755	$42.28	$42.30	$42.30
Purchase #6	$44.56	11.469%	$49.6706	$49.67	$49.65	$49.70
Purchase #7	$41.53	8.497%	$45.0588	$45.06	$45.05	$45.10
7 purchase totals =	$661.90		$722.8490	$722.85	$722.80	$723.00