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	$95.45	9.771%	$104.7764	$104.78	$104.80	$104.80
Purchase #2	$123.27	4.478%	$128.79	$128.79	$128.80	$128.80
Purchase #3	$29.34	12.227%	$32.9274	$32.93	$32.95	$32.90
Purchase #4	$149.61	8.428%	$162.2191	$162.22	$162.20	$162.20
Purchase #5	$18.60	11.709%	$20.7779	$20.78	$20.80	$20.80
Purchase #6	$63.48	3.680%	$65.8161	$65.82	$65.80	$65.80
Purchase #7	$172.62	13.463%	$195.8598	$195.86	$195.85	$195.90
7 purchase totals =	$652.37		$711.1667	$711.18	$711.20	$711.20