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	$96.98	13.345%	$109.922	$109.92	$109.90	$109.90
Purchase #2	$213.38	4.669%	$223.3427	$223.34	$223.35	$223.30
Purchase #3	$32.48	7.701%	$34.9813	$34.98	$35.00	$35.00
Purchase #4	$87.73	13.666%	$99.7192	$99.72	$99.70	$99.70
Purchase #5	$49.47	4.818%	$51.8535	$51.85	$51.85	$51.90
Purchase #6	$116.76	4.333%	$121.8192	$121.82	$121.80	$121.80
Purchase #7	$210.51	8.711%	$228.8475	$228.85	$228.85	$228.80
7 purchase totals =	$807.31		$870.4854	$870.48	$870.45	$870.40