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	$130.42	9.717%	$143.0929	$143.09	$143.10	$143.10
Purchase #2	$78.91	12.380%	$88.6791	$88.68	$88.70	$88.70
Purchase #3	$152.38	9.112%	$166.2649	$166.26	$166.25	$166.30
Purchase #4	$137.99	13.691%	$156.8822	$156.88	$156.90	$156.90
Purchase #5	$125.64	10.766%	$139.1664	$139.17	$139.15	$139.20
Purchase #6	$163.47	5.507%	$172.4723	$172.47	$172.45	$172.50
Purchase #7	$131.33	13.295%	$148.7903	$148.79	$148.80	$148.80
7 purchase totals =	$920.14		$1,015.3481	$1,015.34	$1,015.35	$1,015.50