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	$19.45	7.545%	$20.9175	$20.92	$20.90	$20.90
Purchase #2	$202.91	11.196%	$225.6278	$225.63	$225.65	$225.60
Purchase #3	$56.78	10.358%	$62.6613	$62.66	$62.65	$62.70
Purchase #4	$64.27	11.657%	$71.762	$71.76	$71.75	$71.80
Purchase #5	$215.31	9.333%	$235.4049	$235.40	$235.40	$235.40
Purchase #6	$246.89	5.110%	$259.5061	$259.51	$259.50	$259.50
Purchase #7	$124.86	6.425%	$132.8823	$132.88	$132.90	$132.90
7 purchase totals =	$930.47		$1,008.7619	$1,008.76	$1,008.75	$1,008.80