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	$34.95	11.293%	$38.8969	$38.90	$38.90	$38.90
Purchase #2	$18.80	7.647%	$20.2376	$20.24	$20.25	$20.20
Purchase #3	$82.31	9.869%	$90.4332	$90.43	$90.45	$90.40
Purchase #4	$236.41	11.569%	$263.7603	$263.76	$263.75	$263.80
Purchase #5	$33.83	13.637%	$38.4434	$38.44	$38.45	$38.40
Purchase #6	$146.83	11.846%	$164.2235	$164.22	$164.20	$164.20
Purchase #7	$52.96	11.115%	$58.8465	$58.85	$58.85	$58.80
7 purchase totals =	$606.09		$674.8414	$674.84	$674.85	$674.70