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	$143.46	11.496%	$159.9522	$159.95	$159.95	$160.00
Purchase #2	$41.85	8.606%	$45.4516	$45.45	$45.45	$45.50
Purchase #3	$99.62	9.822%	$109.4047	$109.40	$109.40	$109.40
Purchase #4	$143.56	10.423%	$158.5233	$158.52	$158.50	$158.50
Purchase #5	$42.74	3.741%	$44.3389	$44.34	$44.35	$44.30
Purchase #6	$149.51	13.700%	$169.9929	$169.99	$170.00	$170.00
Purchase #7	$239.57	6.800%	$255.8608	$255.86	$255.85	$255.90
7 purchase totals =	$860.31		$943.5244	$943.51	$943.50	$943.60