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	$101.79	9.813%	$111.7787	$111.78	$111.80	$111.80
Purchase #2	$39.55	6.422%	$42.0899	$42.09	$42.10	$42.10
Purchase #3	$201.44	5.807%	$213.1376	$213.14	$213.15	$213.10
Purchase #4	$52.72	6.321%	$56.0524	$56.05	$56.05	$56.10
Purchase #5	$150.50	6.664%	$160.5293	$160.53	$160.55	$160.50
Purchase #6	$236.54	3.380%	$244.5351	$244.54	$244.55	$244.50
Purchase #7	$152.27	6.187%	$161.6909	$161.69	$161.70	$161.70
7 purchase totals =	$934.81		$989.8139	$989.82	$989.90	$989.80