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	$64.54	12.162%	$72.3894	$72.39	$72.40	$72.40
Purchase #2	$142.39	10.662%	$157.5716	$157.57	$157.55	$157.60
Purchase #3	$101.25	3.484%	$104.7776	$104.78	$104.80	$104.80
Purchase #4	$49.75	6.718%	$53.0922	$53.09	$53.10	$53.10
Purchase #5	$247.66	12.323%	$278.1791	$278.18	$278.20	$278.20
Purchase #6	$176.25	11.338%	$196.2332	$196.23	$196.25	$196.20
Purchase #7	$122.65	13.242%	$138.8913	$138.89	$138.90	$138.90
7 purchase totals =	$904.49		$1,001.1344	$1,001.13	$1,001.20	$1,001.20