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	$39.78	6.788%	$42.4803	$42.48	$42.50	$42.50
Purchase #2	$125.55	9.261%	$137.1772	$137.18	$137.20	$137.20
Purchase #3	$120.93	13.787%	$137.6026	$137.60	$137.60	$137.60
Purchase #4	$199.46	13.872%	$227.1291	$227.13	$227.15	$227.10
Purchase #5	$206.43	3.665%	$213.9957	$214.00	$214.00	$214.00
Purchase #6	$243.34	11.128%	$270.4189	$270.42	$270.40	$270.40
Purchase #7	$134.51	13.214%	$152.2842	$152.28	$152.30	$152.30
7 purchase totals =	$1,070.00		$1,181.0880	$1,181.09	$1,181.15	$1,181.10