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	$30.31	3.249%	$31.2948	$31.29	$31.30	$31.30
Purchase #2	$47.41	10.353%	$52.3184	$52.32	$52.30	$52.30
Purchase #3	$72.84	5.731%	$77.0145	$77.01	$77.00	$77.00
Purchase #4	$192.87	10.579%	$213.2737	$213.27	$213.25	$213.30
Purchase #5	$231.61	3.131%	$238.8617	$238.86	$238.85	$238.90
Purchase #6	$153.58	7.690%	$165.3903	$165.39	$165.40	$165.40
Purchase #7	$163.89	3.412%	$169.4819	$169.48	$169.50	$169.50
7 purchase totals =	$892.51		$947.6353	$947.62	$947.60	$947.70