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	$102.32	5.644%	$108.0949	$108.09	$108.10	$108.10
Purchase #2	$101.48	12.599%	$114.2655	$114.27	$114.25	$114.30
Purchase #3	$247.66	13.495%	$281.0817	$281.08	$281.10	$281.10
Purchase #4	$133.96	12.637%	$150.8885	$150.89	$150.90	$150.90
Purchase #5	$104.41	6.511%	$111.2081	$111.21	$111.20	$111.20
Purchase #6	$178.65	5.787%	$188.9885	$188.99	$189.00	$189.00
Purchase #7	$172.29	7.402%	$185.0429	$185.04	$185.05	$185.00
7 purchase totals =	$1,040.77		$1,139.5701	$1,139.57	$1,139.60	$1,139.60