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	$61.87	6.792%	$66.0722	$66.07	$66.05	$66.10
Purchase #2	$189.95	11.226%	$211.2738	$211.27	$211.25	$211.30
Purchase #3	$237.94	5.222%	$250.3652	$250.37	$250.35	$250.40
Purchase #4	$235.38	9.105%	$256.8113	$256.81	$256.80	$256.80
Purchase #5	$31.44	4.707%	$32.9199	$32.92	$32.90	$32.90
Purchase #6	$126.67	11.389%	$141.0964	$141.10	$141.10	$141.10
Purchase #7	$162.71	4.358%	$169.8009	$169.80	$169.80	$169.80
7 purchase totals =	$1,045.96		$1,128.3397	$1,128.34	$1,128.25	$1,128.40