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	$153.51	4.313%	$160.1309	$160.13	$160.15	$160.10
Purchase #2	$78.83	12.349%	$88.5647	$88.56	$88.55	$88.60
Purchase #3	$142.61	9.813%	$156.6043	$156.60	$156.60	$156.60
Purchase #4	$189.75	13.772%	$215.8824	$215.88	$215.90	$215.90
Purchase #5	$19.72	3.521%	$20.4143	$20.41	$20.40	$20.40
Purchase #6	$45.91	10.273%	$50.6263	$50.63	$50.65	$50.60
Purchase #7	$128.91	8.301%	$139.6108	$139.61	$139.60	$139.60
7 purchase totals =	$759.24		$831.8337	$831.82	$831.85	$831.80