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	$203.25	9.382%	$222.3189	$222.32	$222.30	$222.30
Purchase #2	$89.78	13.280%	$101.7028	$101.70	$101.70	$101.70
Purchase #3	$69.64	9.814%	$76.4745	$76.47	$76.45	$76.50
Purchase #4	$93.54	10.371%	$103.241	$103.24	$103.25	$103.20
Purchase #5	$22.50	10.271%	$24.811	$24.81	$24.80	$24.80
Purchase #6	$56.45	9.499%	$61.8122	$61.81	$61.80	$61.80
Purchase #7	$42.45	10.212%	$46.785	$46.79	$46.80	$46.80
7 purchase totals =	$577.61		$637.1454	$637.14	$637.10	$637.10