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	$20.46	4.735%	$21.4288	$21.43	$21.45	$21.40
Purchase #2	$73.62	13.521%	$83.5742	$83.57	$83.55	$83.60
Purchase #3	$139.96	8.842%	$152.3353	$152.34	$152.35	$152.30
Purchase #4	$105.43	5.575%	$111.3077	$111.31	$111.30	$111.30
Purchase #5	$172.48	6.271%	$183.2962	$183.30	$183.30	$183.30
Purchase #6	$56.27	13.330%	$63.7708	$63.77	$63.75	$63.80
Purchase #7	$117.30	10.664%	$129.8089	$129.81	$129.80	$129.80
7 purchase totals =	$685.52		$745.5219	$745.53	$745.50	$745.50