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	$67.63	9.529%	$74.0745	$74.07	$74.05	$74.10
Purchase #2	$159.44	3.825%	$165.5386	$165.54	$165.55	$165.50
Purchase #3	$106.85	4.408%	$111.5599	$111.56	$111.55	$111.60
Purchase #4	$76.88	9.700%	$84.3374	$84.34	$84.35	$84.30
Purchase #5	$109.59	9.426%	$119.92	$119.92	$119.90	$119.90
Purchase #6	$72.77	8.382%	$78.8696	$78.87	$78.85	$78.90
Purchase #7	$43.98	13.773%	$50.0374	$50.04	$50.05	$50.00
7 purchase totals =	$637.14		$684.3374	$684.34	$684.30	$684.30