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	$170.67	5.630%	$180.2787	$180.28	$180.30	$180.30
Purchase #2	$95.51	4.342%	$99.657	$99.66	$99.65	$99.70
Purchase #3	$92.65	5.411%	$97.6633	$97.66	$97.65	$97.70
Purchase #4	$141.77	13.325%	$160.6609	$160.66	$160.65	$160.70
Purchase #5	$52.49	5.255%	$55.2483	$55.25	$55.25	$55.20
Purchase #6	$192.66	4.270%	$200.8866	$200.89	$200.90	$200.90
Purchase #7	$6.57	7.808%	$7.083	$7.08	$7.10	$7.10
7 purchase totals =	$752.32		$801.4778	$801.48	$801.50	$801.60