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	$99.62	4.659%	$104.2613	$104.26	$104.25	$104.30
Purchase #2	$50.70	7.259%	$54.3803	$54.38	$54.40	$54.40
Purchase #3	$136.26	3.189%	$140.6053	$140.61	$140.60	$140.60
Purchase #4	$243.34	12.531%	$273.8329	$273.83	$273.85	$273.80
Purchase #5	$175.63	6.255%	$186.6157	$186.62	$186.60	$186.60
Purchase #6	$95.39	4.540%	$99.7207	$99.72	$99.70	$99.70
Purchase #7	$215.78	11.218%	$239.9862	$239.99	$240.00	$240.00
7 purchase totals =	$1,016.72		$1,099.4024	$1,099.41	$1,099.40	$1,099.40