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	$84.66	3.708%	$87.7992	$87.80	$87.80	$87.80
Purchase #2	$123.57	10.782%	$136.8933	$136.89	$136.90	$136.90
Purchase #3	$104.52	6.453%	$111.2647	$111.26	$111.25	$111.30
Purchase #4	$95.62	8.313%	$103.5689	$103.57	$103.55	$103.60
Purchase #5	$20.32	6.241%	$21.5882	$21.59	$21.60	$21.60
Purchase #6	$186.44	12.354%	$209.4728	$209.47	$209.45	$209.50
Purchase #7	$33.48	6.514%	$35.6609	$35.66	$35.65	$35.70
7 purchase totals =	$648.61		$706.2480	$706.24	$706.20	$706.40