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	$83.31	8.482%	$90.3764	$90.38	$90.40	$90.40
Purchase #2	$69.26	5.817%	$73.2889	$73.29	$73.30	$73.30
Purchase #3	$228.50	4.553%	$238.9036	$238.90	$238.90	$238.90
Purchase #4	$31.81	9.112%	$34.7085	$34.71	$34.70	$34.70
Purchase #5	$70.40	11.633%	$78.5896	$78.59	$78.60	$78.60
Purchase #6	$137.54	6.147%	$145.9946	$145.99	$146.00	$146.00
Purchase #7	$180.59	6.114%	$191.6313	$191.63	$191.65	$191.60
7 purchase totals =	$801.41		$853.4929	$853.49	$853.55	$853.50