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	$61.98	13.452%	$70.3175	$70.32	$70.30	$70.30
Purchase #2	$103.78	4.654%	$108.6099	$108.61	$108.60	$108.60
Purchase #3	$6.48	8.299%	$7.0178	$7.02	$7.00	$7.00
Purchase #4	$61.96	5.659%	$65.4663	$65.47	$65.45	$65.50
Purchase #5	$70.60	8.498%	$76.5996	$76.60	$76.60	$76.60
Purchase #6	$35.57	13.514%	$40.3769	$40.38	$40.40	$40.40
Purchase #7	$112.52	13.868%	$128.1243	$128.12	$128.10	$128.10
7 purchase totals =	$452.89		$496.5123	$496.52	$496.45	$496.50