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	$214.86	12.301%	$241.2899	$241.29	$241.30	$241.30
Purchase #2	$165.51	9.325%	$180.9438	$180.94	$180.95	$180.90
Purchase #3	$99.91	9.139%	$109.0408	$109.04	$109.05	$109.00
Purchase #4	$212.96	5.561%	$224.8027	$224.80	$224.80	$224.80
Purchase #5	$28.50	10.856%	$31.594	$31.59	$31.60	$31.60
Purchase #6	$33.77	13.474%	$38.3202	$38.32	$38.30	$38.30
Purchase #7	$137.73	6.585%	$146.7995	$146.80	$146.80	$146.80
7 purchase totals =	$893.24		$972.7909	$972.78	$972.80	$972.70