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	$51.86	12.673%	$58.4322	$58.43	$58.45	$58.40
Purchase #2	$92.88	13.204%	$105.1439	$105.14	$105.15	$105.10
Purchase #3	$130.26	7.647%	$140.221	$140.22	$140.20	$140.20
Purchase #4	$5.33	8.472%	$5.7816	$5.78	$5.80	$5.80
Purchase #5	$155.64	7.188%	$166.8274	$166.83	$166.85	$166.80
Purchase #6	$82.44	8.729%	$89.6362	$89.64	$89.65	$89.60
Purchase #7	$192.48	4.234%	$200.6296	$200.63	$200.65	$200.60
7 purchase totals =	$710.89		$766.6719	$766.67	$766.75	$766.50