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	$89.73	4.272%	$93.5633	$93.56	$93.55	$93.60
Purchase #2	$140.58	4.810%	$147.3419	$147.34	$147.35	$147.30
Purchase #3	$156.60	6.455%	$166.7085	$166.71	$166.70	$166.70
Purchase #4	$164.25	9.612%	$180.0377	$180.04	$180.05	$180.00
Purchase #5	$39.67	6.306%	$42.1716	$42.17	$42.15	$42.20
Purchase #6	$50.95	9.529%	$55.805	$55.81	$55.80	$55.80
Purchase #7	$39.44	8.678%	$42.8626	$42.86	$42.85	$42.90
7 purchase totals =	$681.22		$728.4906	$728.49	$728.45	$728.50