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	$192.33	9.242%	$210.1051	$210.11	$210.10	$210.10
Purchase #2	$178.55	6.452%	$190.07	$190.07	$190.05	$190.10
Purchase #3	$31.47	5.143%	$33.0885	$33.09	$33.10	$33.10
Purchase #4	$140.54	13.605%	$159.6605	$159.66	$159.65	$159.70
Purchase #5	$223.33	3.600%	$231.3699	$231.37	$231.35	$231.40
Purchase #6	$56.89	7.259%	$61.0196	$61.02	$61.00	$61.00
Purchase #7	$248.47	12.526%	$279.5934	$279.59	$279.60	$279.60
7 purchase totals =	$1,071.58		$1,164.9070	$1,164.91	$1,164.85	$1,165.00