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	$43.27	8.145%	$46.7943	$46.79	$46.80	$46.80
Purchase #2	$105.81	13.361%	$119.9473	$119.95	$119.95	$119.90
Purchase #3	$227.77	9.393%	$249.1644	$249.16	$249.15	$249.20
Purchase #4	$94.69	5.144%	$99.5609	$99.56	$99.55	$99.60
Purchase #5	$35.59	4.832%	$37.3097	$37.31	$37.30	$37.30
Purchase #6	$81.35	3.854%	$84.4852	$84.49	$84.50	$84.50
Purchase #7	$62.46	5.730%	$66.039	$66.04	$66.05	$66.00
7 purchase totals =	$650.94		$703.3008	$703.30	$703.30	$703.30