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	$48.39	8.194%	$52.3551	$52.36	$52.35	$52.40
Purchase #2	$198.62	11.168%	$220.8019	$220.80	$220.80	$220.80
Purchase #3	$137.79	13.215%	$155.9989	$156.00	$156.00	$156.00
Purchase #4	$238.48	7.481%	$256.3207	$256.32	$256.30	$256.30
Purchase #5	$92.53	10.736%	$102.464	$102.46	$102.45	$102.50
Purchase #6	$37.83	7.695%	$40.741	$40.74	$40.75	$40.70
Purchase #7	$35.93	7.131%	$38.4922	$38.49	$38.50	$38.50
7 purchase totals =	$789.57		$867.1738	$867.17	$867.15	$867.20