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	$164.87	6.447%	$175.4992	$175.50	$175.50	$175.50
Purchase #2	$75.48	13.324%	$85.537	$85.54	$85.55	$85.50
Purchase #3	$118.32	6.763%	$126.322	$126.32	$126.30	$126.30
Purchase #4	$52.30	5.863%	$55.3663	$55.37	$55.35	$55.40
Purchase #5	$71.67	12.755%	$80.8115	$80.81	$80.80	$80.80
Purchase #6	$90.45	6.266%	$96.1176	$96.12	$96.10	$96.10
Purchase #7	$19.40	10.358%	$21.4095	$21.41	$21.40	$21.40
7 purchase totals =	$592.49		$641.0631	$641.07	$641.00	$641.00