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	$15.52	12.277%	$17.4254	$17.43	$17.45	$17.40
Purchase #2	$189.79	12.724%	$213.9389	$213.94	$213.95	$213.90
Purchase #3	$11.28	9.146%	$12.3117	$12.31	$12.30	$12.30
Purchase #4	$66.67	11.473%	$74.319	$74.32	$74.30	$74.30
Purchase #5	$246.83	11.339%	$274.8181	$274.82	$274.80	$274.80
Purchase #6	$173.90	12.743%	$196.0601	$196.06	$196.05	$196.10
Purchase #7	$33.66	11.242%	$37.4441	$37.44	$37.45	$37.40
7 purchase totals =	$737.65		$826.3173	$826.32	$826.30	$826.20