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	$72.78	7.531%	$78.2611	$78.26	$78.25	$78.30
Purchase #2	$27.84	7.531%	$29.9366	$29.94	$29.95	$29.90
Purchase #3	$65.76	12.189%	$73.7755	$73.78	$73.80	$73.80
Purchase #4	$73.55	3.241%	$75.9338	$75.93	$75.95	$75.90
Purchase #5	$69.88	10.851%	$77.4627	$77.46	$77.45	$77.50
Purchase #6	$197.72	12.217%	$221.8755	$221.88	$221.90	$221.90
Purchase #7	$164.61	12.538%	$185.2488	$185.25	$185.25	$185.20
7 purchase totals =	$672.14		$742.4940	$742.50	$742.55	$742.50