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	$55.29	9.184%	$60.3678	$60.37	$60.35	$60.40
Purchase #2	$37.67	13.264%	$42.6665	$42.67	$42.65	$42.70
Purchase #3	$247.36	3.670%	$256.4381	$256.44	$256.45	$256.40
Purchase #4	$69.69	5.137%	$73.27	$73.27	$73.25	$73.30
Purchase #5	$128.59	7.641%	$138.4156	$138.42	$138.40	$138.40
Purchase #6	$43.40	11.425%	$48.3585	$48.36	$48.35	$48.40
Purchase #7	$142.60	5.787%	$150.8523	$150.85	$150.85	$150.90
7 purchase totals =	$724.60		$770.3688	$770.38	$770.30	$770.50