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	$36.73	9.776%	$40.3207	$40.32	$40.30	$40.30
Purchase #2	$146.85	7.252%	$157.4996	$157.50	$157.50	$157.50
Purchase #3	$17.41	8.463%	$18.8834	$18.88	$18.90	$18.90
Purchase #4	$191.53	4.602%	$200.3442	$200.34	$200.35	$200.30
Purchase #5	$123.27	11.643%	$137.6223	$137.62	$137.60	$137.60
Purchase #6	$237.78	4.860%	$249.3361	$249.34	$249.35	$249.30
Purchase #7	$124.36	11.429%	$138.5731	$138.57	$138.55	$138.60
7 purchase totals =	$877.93		$942.5794	$942.57	$942.55	$942.50