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	$117.71	5.777%	$124.5101	$124.51	$124.50	$124.50
Purchase #2	$87.40	4.506%	$91.3382	$91.34	$91.35	$91.30
Purchase #3	$119.53	12.172%	$134.0792	$134.08	$134.10	$134.10
Purchase #4	$52.67	10.666%	$58.2878	$58.29	$58.30	$58.30
Purchase #5	$87.33	4.169%	$90.9708	$90.97	$90.95	$91.00
Purchase #6	$120.76	5.778%	$127.7375	$127.74	$127.75	$127.70
Purchase #7	$42.42	6.348%	$45.1128	$45.11	$45.10	$45.10
7 purchase totals =	$627.82		$672.0364	$672.04	$672.05	$672.00