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	$30.25	5.228%	$31.8315	$31.83	$31.85	$31.80
Purchase #2	$146.52	8.806%	$159.4226	$159.42	$159.40	$159.40
Purchase #3	$49.69	11.446%	$55.3775	$55.38	$55.40	$55.40
Purchase #4	$174.27	3.392%	$180.1812	$180.18	$180.20	$180.20
Purchase #5	$33.97	4.714%	$35.5713	$35.57	$35.55	$35.60
Purchase #6	$150.33	6.215%	$159.673	$159.67	$159.65	$159.70
Purchase #7	$228.55	11.726%	$255.3498	$255.35	$255.35	$255.30
7 purchase totals =	$813.58		$877.4069	$877.40	$877.40	$877.40