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	$22.63	9.824%	$24.8532	$24.85	$24.85	$24.90
Purchase #2	$100.85	4.525%	$105.4135	$105.41	$105.40	$105.40
Purchase #3	$112.77	13.409%	$127.8913	$127.89	$127.90	$127.90
Purchase #4	$71.28	13.425%	$80.8493	$80.85	$80.85	$80.80
Purchase #5	$200.52	10.634%	$221.8433	$221.84	$221.85	$221.80
Purchase #6	$97.98	7.639%	$105.4647	$105.46	$105.45	$105.50
Purchase #7	$71.78	13.719%	$81.6275	$81.63	$81.65	$81.60
7 purchase totals =	$677.81		$747.9428	$747.93	$747.95	$747.90