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	$67.78	6.117%	$71.9261	$71.93	$71.95	$71.90
Purchase #2	$44.80	8.241%	$48.492	$48.49	$48.50	$48.50
Purchase #3	$155.69	12.689%	$175.4455	$175.45	$175.45	$175.40
Purchase #4	$40.86	4.569%	$42.7269	$42.73	$42.75	$42.70
Purchase #5	$227.74	9.842%	$250.1542	$250.15	$250.15	$250.20
Purchase #6	$205.78	8.730%	$223.7446	$223.74	$223.75	$223.70
Purchase #7	$17.47	10.847%	$19.365	$19.37	$19.35	$19.40
7 purchase totals =	$760.12		$831.8543	$831.86	$831.90	$831.80