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	$31.75	11.375%	$35.3616	$35.36	$35.35	$35.40
Purchase #2	$250.82	8.262%	$271.5427	$271.54	$271.55	$271.50
Purchase #3	$102.34	13.390%	$116.0433	$116.04	$116.05	$116.00
Purchase #4	$175.79	7.592%	$189.136	$189.14	$189.15	$189.10
Purchase #5	$81.63	11.341%	$90.8877	$90.89	$90.90	$90.90
Purchase #6	$20.38	3.102%	$21.0122	$21.01	$21.00	$21.00
Purchase #7	$170.91	5.678%	$180.6143	$180.61	$180.60	$180.60
7 purchase totals =	$833.62		$904.5978	$904.59	$904.60	$904.50