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	$102.84	8.313%	$111.3891	$111.39	$111.40	$111.40
Purchase #2	$85.68	6.308%	$91.0847	$91.08	$91.10	$91.10
Purchase #3	$75.54	3.800%	$78.4105	$78.41	$78.40	$78.40
Purchase #4	$151.86	6.112%	$161.1417	$161.14	$161.15	$161.10
Purchase #5	$159.41	6.499%	$169.7701	$169.77	$169.75	$169.80
Purchase #6	$42.48	12.259%	$47.6876	$47.69	$47.70	$47.70
Purchase #7	$13.38	6.334%	$14.2275	$14.23	$14.25	$14.20
7 purchase totals =	$631.19		$673.7112	$673.71	$673.75	$673.70