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	$142.94	13.259%	$161.8924	$161.89	$161.90	$161.90
Purchase #2	$203.80	8.417%	$220.9538	$220.95	$220.95	$221.00
Purchase #3	$125.79	12.811%	$141.905	$141.91	$141.90	$141.90
Purchase #4	$120.82	8.748%	$131.3893	$131.39	$131.40	$131.40
Purchase #5	$130.25	8.820%	$141.7381	$141.74	$141.75	$141.70
Purchase #6	$100.90	13.841%	$114.8656	$114.87	$114.85	$114.90
Purchase #7	$170.80	12.709%	$192.507	$192.51	$192.50	$192.50
7 purchase totals =	$995.30		$1,105.2512	$1,105.26	$1,105.25	$1,105.30