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	$182.98	12.674%	$206.1709	$206.17	$206.15	$206.20
Purchase #2	$104.34	11.528%	$116.3683	$116.37	$116.35	$116.40
Purchase #3	$31.74	10.438%	$35.053	$35.05	$35.05	$35.10
Purchase #4	$85.29	6.303%	$90.6658	$90.67	$90.65	$90.70
Purchase #5	$34.38	13.400%	$38.9869	$38.99	$39.00	$39.00
Purchase #6	$95.75	4.142%	$99.716	$99.72	$99.70	$99.70
Purchase #7	$182.28	10.220%	$200.909	$200.91	$200.90	$200.90
7 purchase totals =	$716.76		$787.8699	$787.88	$787.80	$788.00