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	$37.90	3.131%	$39.0866	$39.09	$39.10	$39.10
Purchase #2	$49.81	5.367%	$52.4833	$52.48	$52.50	$52.50
Purchase #3	$48.62	10.792%	$53.8671	$53.87	$53.85	$53.90
Purchase #4	$86.31	5.490%	$91.0484	$91.05	$91.05	$91.00
Purchase #5	$234.67	3.524%	$242.9398	$242.94	$242.95	$242.90
Purchase #6	$220.94	10.783%	$244.764	$244.76	$244.75	$244.80
Purchase #7	$167.29	13.810%	$190.3927	$190.39	$190.40	$190.40
7 purchase totals =	$845.54		$914.5819	$914.58	$914.60	$914.60