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	$22.73	13.134%	$25.7154	$25.72	$25.70	$25.70
Purchase #2	$140.66	13.216%	$159.2496	$159.25	$159.25	$159.20
Purchase #3	$91.26	10.332%	$100.689	$100.69	$100.70	$100.70
Purchase #4	$161.50	11.823%	$180.5941	$180.59	$180.60	$180.60
Purchase #5	$65.94	9.199%	$72.0058	$72.01	$72.00	$72.00
Purchase #6	$49.77	12.313%	$55.8982	$55.90	$55.90	$55.90
Purchase #7	$143.35	11.251%	$159.4783	$159.48	$159.50	$159.50
7 purchase totals =	$675.21		$753.6304	$753.64	$753.65	$753.60