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	$72.74	7.590%	$78.261	$78.26	$78.25	$78.30
Purchase #2	$154.60	8.825%	$168.2435	$168.24	$168.25	$168.20
Purchase #3	$28.64	9.831%	$31.4556	$31.46	$31.45	$31.50
Purchase #4	$101.34	12.408%	$113.9143	$113.91	$113.90	$113.90
Purchase #5	$85.42	6.201%	$90.7169	$90.72	$90.70	$90.70
Purchase #6	$121.74	7.797%	$131.2321	$131.23	$131.25	$131.20
Purchase #7	$54.88	7.314%	$58.8939	$58.89	$58.90	$58.90
7 purchase totals =	$619.36		$672.7173	$672.71	$672.70	$672.70