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	$130.62	10.258%	$144.019	$144.02	$144.00	$144.00
Purchase #2	$192.27	3.785%	$199.5474	$199.55	$199.55	$199.50
Purchase #3	$40.88	4.659%	$42.7846	$42.78	$42.80	$42.80
Purchase #4	$237.70	11.233%	$264.4008	$264.40	$264.40	$264.40
Purchase #5	$85.35	7.394%	$91.6608	$91.66	$91.65	$91.70
Purchase #6	$166.38	11.222%	$185.0512	$185.05	$185.05	$185.10
Purchase #7	$28.39	9.606%	$31.1171	$31.12	$31.10	$31.10
7 purchase totals =	$881.59		$958.5809	$958.58	$958.55	$958.60