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	$152.31	5.271%	$160.3383	$160.34	$160.35	$160.30
Purchase #2	$92.85	10.400%	$102.5064	$102.51	$102.50	$102.50
Purchase #3	$54.75	9.536%	$59.971	$59.97	$59.95	$60.00
Purchase #4	$90.75	3.660%	$94.0715	$94.07	$94.05	$94.10
Purchase #5	$93.84	6.311%	$99.7622	$99.76	$99.75	$99.80
Purchase #6	$178.53	12.512%	$200.8677	$200.87	$200.85	$200.90
Purchase #7	$218.54	3.354%	$225.8698	$225.87	$225.85	$225.90
7 purchase totals =	$881.57		$943.3869	$943.39	$943.30	$943.50