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	$121.34	11.249%	$134.9895	$134.99	$135.00	$135.00
Purchase #2	$90.69	6.523%	$96.6057	$96.61	$96.60	$96.60
Purchase #3	$103.98	4.742%	$108.9107	$108.91	$108.90	$108.90
Purchase #4	$88.35	12.807%	$99.665	$99.67	$99.65	$99.70
Purchase #5	$208.88	6.595%	$222.6556	$222.66	$222.65	$222.70
Purchase #6	$141.88	4.659%	$148.4902	$148.49	$148.50	$148.50
Purchase #7	$127.84	11.669%	$142.7576	$142.76	$142.75	$142.80
7 purchase totals =	$882.96		$954.0743	$954.09	$954.05	$954.20