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	$77.58	5.232%	$81.639	$81.64	$81.65	$81.60
Purchase #2	$196.55	13.734%	$223.5442	$223.54	$223.55	$223.50
Purchase #3	$22.30	8.281%	$24.1467	$24.15	$24.15	$24.10
Purchase #4	$37.89	6.314%	$40.2824	$40.28	$40.30	$40.30
Purchase #5	$56.82	3.760%	$58.9564	$58.96	$58.95	$59.00
Purchase #6	$172.81	10.728%	$191.3491	$191.35	$191.35	$191.30
Purchase #7	$247.79	13.453%	$281.1252	$281.13	$281.15	$281.10
7 purchase totals =	$811.74		$901.0430	$901.05	$901.10	$900.90