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	$116.90	3.295%	$120.7519	$120.75	$120.75	$120.80
Purchase #2	$118.41	6.225%	$125.781	$125.78	$125.80	$125.80
Purchase #3	$127.48	4.767%	$133.557	$133.56	$133.55	$133.60
Purchase #4	$32.94	12.333%	$37.0025	$37.00	$37.00	$37.00
Purchase #5	$210.53	5.307%	$221.7028	$221.70	$221.70	$221.70
Purchase #6	$225.45	13.757%	$256.4652	$256.47	$256.45	$256.50
Purchase #7	$96.83	3.390%	$100.1125	$100.11	$100.10	$100.10
7 purchase totals =	$928.54		$995.3729	$995.37	$995.35	$995.50