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	$35.41	4.794%	$37.1076	$37.11	$37.10	$37.10
Purchase #2	$123.52	11.434%	$137.6433	$137.64	$137.65	$137.60
Purchase #3	$192.89	3.607%	$199.8475	$199.85	$199.85	$199.80
Purchase #4	$98.89	3.824%	$102.6716	$102.67	$102.65	$102.70
Purchase #5	$17.61	6.136%	$18.6905	$18.69	$18.70	$18.70
Purchase #6	$42.87	13.845%	$48.8054	$48.81	$48.80	$48.80
Purchase #7	$40.31	8.835%	$43.8714	$43.87	$43.85	$43.90
7 purchase totals =	$551.50		$588.6373	$588.64	$588.60	$588.60