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	$114.90	13.223%	$130.0932	$130.09	$130.10	$130.10
Purchase #2	$169.46	12.250%	$190.2189	$190.22	$190.20	$190.20
Purchase #3	$190.64	13.443%	$216.2677	$216.27	$216.25	$216.30
Purchase #4	$37.91	9.728%	$41.5979	$41.60	$41.60	$41.60
Purchase #5	$100.52	10.321%	$110.8947	$110.89	$110.90	$110.90
Purchase #6	$28.57	5.667%	$30.1891	$30.19	$30.20	$30.20
Purchase #7	$38.90	6.548%	$41.4472	$41.45	$41.45	$41.40
7 purchase totals =	$680.90		$760.7087	$760.71	$760.70	$760.70