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	$127.46	12.349%	$143.2	$143.20	$143.20	$143.20
Purchase #2	$210.97	12.406%	$237.1429	$237.14	$237.15	$237.10
Purchase #3	$136.98	10.503%	$151.367	$151.37	$151.35	$151.40
Purchase #4	$81.69	13.669%	$92.8562	$92.86	$92.85	$92.90
Purchase #5	$152.40	11.141%	$169.3789	$169.38	$169.40	$169.40
Purchase #6	$116.88	12.215%	$131.1569	$131.16	$131.15	$131.20
Purchase #7	$30.50	13.473%	$34.6093	$34.61	$34.60	$34.60
7 purchase totals =	$856.88		$959.7112	$959.72	$959.70	$959.80