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	$155.48	13.202%	$176.0065	$176.01	$176.00	$176.00
Purchase #2	$18.87	10.466%	$20.8449	$20.84	$20.85	$20.80
Purchase #3	$223.61	13.581%	$253.9785	$253.98	$254.00	$254.00
Purchase #4	$112.58	9.643%	$123.4361	$123.44	$123.45	$123.40
Purchase #5	$21.70	5.320%	$22.8544	$22.85	$22.85	$22.90
Purchase #6	$143.71	6.313%	$152.7824	$152.78	$152.80	$152.80
Purchase #7	$59.33	12.234%	$66.5884	$66.59	$66.60	$66.60
7 purchase totals =	$735.28		$816.4912	$816.49	$816.55	$816.50