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	$150.58	13.231%	$170.5032	$170.50	$170.50	$170.50
Purchase #2	$93.63	11.310%	$104.2196	$104.22	$104.20	$104.20
Purchase #3	$35.39	11.643%	$39.5105	$39.51	$39.50	$39.50
Purchase #4	$193.76	13.175%	$219.2879	$219.29	$219.30	$219.30
Purchase #5	$121.45	4.186%	$126.5339	$126.53	$126.55	$126.50
Purchase #6	$126.88	12.234%	$142.4025	$142.40	$142.40	$142.40
Purchase #7	$29.76	12.333%	$33.4303	$33.43	$33.45	$33.40
7 purchase totals =	$751.45		$835.8879	$835.88	$835.90	$835.80