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	$138.35	6.667%	$147.5738	$147.57	$147.55	$147.60
Purchase #2	$213.93	3.673%	$221.7876	$221.79	$221.80	$221.80
Purchase #3	$158.53	10.393%	$175.006	$175.01	$175.00	$175.00
Purchase #4	$152.67	10.720%	$169.0362	$169.04	$169.05	$169.00
Purchase #5	$93.78	5.724%	$99.148	$99.15	$99.15	$99.10
Purchase #6	$38.77	6.188%	$41.1691	$41.17	$41.15	$41.20
Purchase #7	$117.48	8.619%	$127.6056	$127.61	$127.60	$127.60
7 purchase totals =	$913.51		$981.3263	$981.34	$981.30	$981.30