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	$130.67	5.634%	$138.0319	$138.03	$138.05	$138.00
Purchase #2	$35.83	13.759%	$40.7598	$40.76	$40.75	$40.80
Purchase #3	$247.72	8.162%	$267.9389	$267.94	$267.95	$267.90
Purchase #4	$43.33	8.848%	$47.1638	$47.16	$47.15	$47.20
Purchase #5	$154.59	11.385%	$172.1901	$172.19	$172.20	$172.20
Purchase #6	$52.46	3.821%	$54.4645	$54.46	$54.45	$54.50
Purchase #7	$41.38	9.341%	$45.2453	$45.25	$45.25	$45.20
7 purchase totals =	$705.98		$765.7943	$765.79	$765.80	$765.80