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	$28.62	11.293%	$31.8521	$31.85	$31.85	$31.90
Purchase #2	$99.42	11.326%	$110.6803	$110.68	$110.70	$110.70
Purchase #3	$131.38	13.123%	$148.621	$148.62	$148.60	$148.60
Purchase #4	$63.62	12.832%	$71.7837	$71.78	$71.80	$71.80
Purchase #5	$218.93	13.303%	$248.0543	$248.05	$248.05	$248.10
Purchase #6	$190.49	9.324%	$208.2513	$208.25	$208.25	$208.30
Purchase #7	$80.37	12.491%	$90.409	$90.41	$90.40	$90.40
7 purchase totals =	$812.83		$909.6517	$909.64	$909.65	$909.80