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	$123.50	8.119%	$133.527	$133.53	$133.55	$133.50
Purchase #2	$122.81	7.409%	$131.909	$131.91	$131.90	$131.90
Purchase #3	$153.39	11.671%	$171.2921	$171.29	$171.30	$171.30
Purchase #4	$161.72	13.598%	$183.7107	$183.71	$183.70	$183.70
Purchase #5	$152.38	10.348%	$168.1483	$168.15	$168.15	$168.10
Purchase #6	$131.38	11.258%	$146.1708	$146.17	$146.15	$146.20
Purchase #7	$247.62	12.500%	$278.5725	$278.57	$278.55	$278.60
7 purchase totals =	$1,092.80		$1,213.3304	$1,213.33	$1,213.30	$1,213.30