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	$239.47	4.536%	$250.3324	$250.33	$250.35	$250.30
Purchase #2	$165.77	13.686%	$188.4573	$188.46	$188.45	$188.50
Purchase #3	$108.25	12.693%	$121.9902	$121.99	$122.00	$122.00
Purchase #4	$91.61	10.151%	$100.9093	$100.91	$100.90	$100.90
Purchase #5	$176.64	7.225%	$189.4022	$189.40	$189.40	$189.40
Purchase #6	$37.56	7.318%	$40.3086	$40.31	$40.30	$40.30
Purchase #7	$143.99	5.484%	$151.8864	$151.89	$151.90	$151.90
7 purchase totals =	$963.29		$1,043.2864	$1,043.29	$1,043.30	$1,043.30