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	$111.85	11.622%	$124.8492	$124.85	$124.85	$124.80
Purchase #2	$62.68	12.421%	$70.4655	$70.47	$70.45	$70.50
Purchase #3	$130.86	11.805%	$146.308	$146.31	$146.30	$146.30
Purchase #4	$36.80	5.226%	$38.7232	$38.72	$38.70	$38.70
Purchase #5	$227.56	7.123%	$243.7691	$243.77	$243.75	$243.80
Purchase #6	$129.83	8.323%	$140.6358	$140.64	$140.65	$140.60
Purchase #7	$79.31	12.658%	$89.3491	$89.35	$89.35	$89.30
7 purchase totals =	$778.89		$854.0999	$854.11	$854.05	$854.00