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	$170.75	4.529%	$178.4833	$178.48	$178.50	$178.50
Purchase #2	$84.97	12.810%	$95.8547	$95.85	$95.85	$95.90
Purchase #3	$214.74	4.257%	$223.8815	$223.88	$223.90	$223.90
Purchase #4	$32.44	12.393%	$36.4603	$36.46	$36.45	$36.50
Purchase #5	$136.99	10.662%	$151.5959	$151.60	$151.60	$151.60
Purchase #6	$143.44	13.561%	$162.8919	$162.89	$162.90	$162.90
Purchase #7	$198.99	9.369%	$217.6334	$217.63	$217.65	$217.60
7 purchase totals =	$982.32		$1,066.8010	$1,066.79	$1,066.85	$1,066.90