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	$28.68	10.457%	$31.6791	$31.68	$31.70	$31.70
Purchase #2	$134.88	13.605%	$153.2304	$153.23	$153.25	$153.20
Purchase #3	$106.42	13.590%	$120.8825	$120.88	$120.90	$120.90
Purchase #4	$165.43	4.201%	$172.3797	$172.38	$172.40	$172.40
Purchase #5	$17.90	4.543%	$18.7132	$18.71	$18.70	$18.70
Purchase #6	$35.90	3.103%	$37.014	$37.01	$37.00	$37.00
Purchase #7	$196.91	6.164%	$209.0475	$209.05	$209.05	$209.00
7 purchase totals =	$686.12		$742.9464	$742.94	$743.00	$742.90