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	$72.34	13.868%	$82.3721	$82.37	$82.35	$82.40
Purchase #2	$52.54	9.363%	$57.4593	$57.46	$57.45	$57.50
Purchase #3	$60.61	6.302%	$64.4296	$64.43	$64.45	$64.40
Purchase #4	$71.73	12.473%	$80.6769	$80.68	$80.70	$80.70
Purchase #5	$113.71	5.632%	$120.1141	$120.11	$120.10	$120.10
Purchase #6	$111.42	4.297%	$116.2077	$116.21	$116.20	$116.20
Purchase #7	$11.68	5.270%	$12.2955	$12.30	$12.30	$12.30
7 purchase totals =	$494.03		$533.5552	$533.56	$533.55	$533.60