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	$16.67	13.570%	$18.9321	$18.93	$18.95	$18.90
Purchase #2	$38.81	3.681%	$40.2386	$40.24	$40.25	$40.20
Purchase #3	$52.77	6.681%	$56.2956	$56.30	$56.30	$56.30
Purchase #4	$169.88	10.837%	$188.2899	$188.29	$188.30	$188.30
Purchase #5	$213.93	3.371%	$221.1416	$221.14	$221.15	$221.10
Purchase #6	$56.68	4.566%	$59.268	$59.27	$59.25	$59.30
Purchase #7	$140.87	13.110%	$159.3381	$159.34	$159.35	$159.30
7 purchase totals =	$689.61		$743.5039	$743.51	$743.55	$743.40