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	$21.96	10.696%	$24.3088	$24.31	$24.30	$24.30
Purchase #2	$156.95	6.562%	$167.2491	$167.25	$167.25	$167.20
Purchase #3	$81.46	10.679%	$90.1591	$90.16	$90.15	$90.20
Purchase #4	$242.71	13.304%	$275.0001	$275.00	$275.00	$275.00
Purchase #5	$59.39	12.578%	$66.8601	$66.86	$66.85	$66.90
Purchase #6	$243.63	12.256%	$273.4893	$273.49	$273.50	$273.50
Purchase #7	$134.41	6.125%	$142.6426	$142.64	$142.65	$142.60
7 purchase totals =	$940.51		$1,039.7091	$1,039.71	$1,039.70	$1,039.70