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	$87.42	3.525%	$90.5016	$90.50	$90.50	$90.50
Purchase #2	$130.76	7.575%	$140.6651	$140.67	$140.65	$140.70
Purchase #3	$173.76	3.596%	$180.0084	$180.01	$180.00	$180.00
Purchase #4	$31.74	11.792%	$35.4828	$35.48	$35.50	$35.50
Purchase #5	$20.90	3.650%	$21.6629	$21.66	$21.65	$21.70
Purchase #6	$161.90	4.688%	$169.4899	$169.49	$169.50	$169.50
Purchase #7	$172.40	9.540%	$188.847	$188.85	$188.85	$188.80
7 purchase totals =	$778.88		$826.6577	$826.66	$826.65	$826.70