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	$149.59	4.190%	$155.8578	$155.86	$155.85	$155.90
Purchase #2	$31.37	3.509%	$32.4708	$32.47	$32.45	$32.50
Purchase #3	$141.52	6.659%	$150.9438	$150.94	$150.95	$150.90
Purchase #4	$9.65	9.364%	$10.5536	$10.55	$10.55	$10.60
Purchase #5	$38.66	5.642%	$40.8412	$40.84	$40.85	$40.80
Purchase #6	$87.44	3.518%	$90.5161	$90.52	$90.50	$90.50
Purchase #7	$61.34	12.749%	$69.1602	$69.16	$69.15	$69.20
7 purchase totals =	$519.57		$550.3435	$550.34	$550.30	$550.40