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	$18.71	13.105%	$21.1619	$21.16	$21.15	$21.20
Purchase #2	$87.91	12.655%	$99.035	$99.04	$99.05	$99.00
Purchase #3	$128.94	12.294%	$144.7919	$144.79	$144.80	$144.80
Purchase #4	$228.78	5.837%	$242.1339	$242.13	$242.15	$242.10
Purchase #5	$127.34	8.738%	$138.467	$138.47	$138.45	$138.50
Purchase #6	$134.59	7.667%	$144.909	$144.91	$144.90	$144.90
Purchase #7	$215.70	8.775%	$234.6277	$234.63	$234.65	$234.60
7 purchase totals =	$941.97		$1,025.1264	$1,025.13	$1,025.15	$1,025.10