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	$143.34	12.308%	$160.9823	$160.98	$161.00	$161.00
Purchase #2	$72.64	12.348%	$81.6096	$81.61	$81.60	$81.60
Purchase #3	$210.59	9.663%	$230.9393	$230.94	$230.95	$230.90
Purchase #4	$59.25	4.704%	$62.0371	$62.04	$62.05	$62.00
Purchase #5	$86.34	13.786%	$98.2428	$98.24	$98.25	$98.20
Purchase #6	$18.59	9.395%	$20.3365	$20.34	$20.35	$20.30
Purchase #7	$130.73	5.452%	$137.8574	$137.86	$137.85	$137.90
7 purchase totals =	$721.48		$792.0050	$792.01	$792.05	$791.90