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	$153.65	10.749%	$170.1658	$170.17	$170.15	$170.20
Purchase #2	$77.38	8.333%	$83.8281	$83.83	$83.85	$83.80
Purchase #3	$126.67	7.726%	$136.4565	$136.46	$136.45	$136.50
Purchase #4	$86.39	4.788%	$90.5264	$90.53	$90.55	$90.50
Purchase #5	$37.30	4.200%	$38.8666	$38.87	$38.85	$38.90
Purchase #6	$31.51	12.642%	$35.4935	$35.49	$35.50	$35.50
Purchase #7	$92.93	8.389%	$100.7259	$100.73	$100.75	$100.70
7 purchase totals =	$605.83		$656.0628	$656.08	$656.10	$656.10