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	$140.80	8.123%	$152.2372	$152.24	$152.25	$152.20
Purchase #2	$203.37	10.743%	$225.218	$225.22	$225.20	$225.20
Purchase #3	$60.33	9.530%	$66.0794	$66.08	$66.10	$66.10
Purchase #4	$57.71	13.401%	$65.4437	$65.44	$65.45	$65.40
Purchase #5	$10.47	4.225%	$10.9124	$10.91	$10.90	$10.90
Purchase #6	$201.92	12.803%	$227.7718	$227.77	$227.75	$227.80
Purchase #7	$86.46	3.540%	$89.5207	$89.52	$89.50	$89.50
7 purchase totals =	$761.06		$837.1832	$837.18	$837.15	$837.10