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	$150.36	10.660%	$166.3884	$166.39	$166.40	$166.40
Purchase #2	$51.89	6.786%	$55.4113	$55.41	$55.40	$55.40
Purchase #3	$212.61	3.241%	$219.5007	$219.50	$219.50	$219.50
Purchase #4	$201.28	10.257%	$221.9253	$221.93	$221.95	$221.90
Purchase #5	$87.35	3.418%	$90.3356	$90.34	$90.35	$90.30
Purchase #6	$55.62	7.468%	$59.7737	$59.77	$59.75	$59.80
Purchase #7	$15.90	8.512%	$17.2534	$17.25	$17.25	$17.30
7 purchase totals =	$775.01		$830.5884	$830.59	$830.60	$830.60