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	$34.84	4.690%	$36.474	$36.47	$36.45	$36.50
Purchase #2	$230.82	12.686%	$260.1018	$260.10	$260.10	$260.10
Purchase #3	$207.98	6.390%	$221.2699	$221.27	$221.25	$221.30
Purchase #4	$53.37	11.618%	$59.5705	$59.57	$59.55	$59.60
Purchase #5	$129.32	7.587%	$139.1315	$139.13	$139.15	$139.10
Purchase #6	$196.45	12.358%	$220.7273	$220.73	$220.75	$220.70
Purchase #7	$70.89	13.198%	$80.2461	$80.25	$80.25	$80.20
7 purchase totals =	$923.67		$1,017.5211	$1,017.52	$1,017.50	$1,017.50