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	$13.38	3.388%	$13.8333	$13.83	$13.85	$13.80
Purchase #2	$172.95	7.741%	$186.3381	$186.34	$186.35	$186.30
Purchase #3	$195.26	11.251%	$217.2287	$217.23	$217.25	$217.20
Purchase #4	$242.44	13.342%	$274.7863	$274.79	$274.80	$274.80
Purchase #5	$63.53	6.124%	$67.4206	$67.42	$67.40	$67.40
Purchase #6	$105.40	13.655%	$119.7924	$119.79	$119.80	$119.80
Purchase #7	$79.85	13.492%	$90.6234	$90.62	$90.60	$90.60
7 purchase totals =	$872.81		$970.0228	$970.02	$970.05	$969.90