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	$115.72	10.655%	$128.05	$128.05	$128.05	$128.10
Purchase #2	$20.60	6.361%	$21.9104	$21.91	$21.90	$21.90
Purchase #3	$95.73	4.485%	$100.0235	$100.02	$100.00	$100.00
Purchase #4	$38.71	4.137%	$40.3114	$40.31	$40.30	$40.30
Purchase #5	$31.45	12.386%	$35.3454	$35.35	$35.35	$35.30
Purchase #6	$113.74	8.864%	$123.8219	$123.82	$123.80	$123.80
Purchase #7	$44.83	5.565%	$47.3248	$47.32	$47.30	$47.30
7 purchase totals =	$460.78		$496.7874	$496.78	$496.70	$496.70