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	$109.34	11.121%	$121.4997	$121.50	$121.50	$121.50
Purchase #2	$213.94	10.510%	$236.4251	$236.43	$236.45	$236.40
Purchase #3	$190.87	11.709%	$213.219	$213.22	$213.20	$213.20
Purchase #4	$40.29	8.268%	$43.6212	$43.62	$43.60	$43.60
Purchase #5	$66.94	4.637%	$70.044	$70.04	$70.05	$70.00
Purchase #6	$123.45	3.552%	$127.8349	$127.83	$127.85	$127.80
Purchase #7	$184.77	6.530%	$196.8355	$196.84	$196.85	$196.80
7 purchase totals =	$929.60		$1,009.4794	$1,009.48	$1,009.50	$1,009.30