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	$114.71	4.430%	$119.7917	$119.79	$119.80	$119.80
Purchase #2	$35.96	9.702%	$39.4488	$39.45	$39.45	$39.40
Purchase #3	$64.62	12.795%	$72.8881	$72.89	$72.90	$72.90
Purchase #4	$249.41	11.230%	$277.4187	$277.42	$277.40	$277.40
Purchase #5	$99.46	12.419%	$111.8119	$111.81	$111.80	$111.80
Purchase #6	$35.68	5.471%	$37.6321	$37.63	$37.65	$37.60
Purchase #7	$231.96	11.207%	$257.9558	$257.96	$257.95	$258.00
7 purchase totals =	$831.80		$916.9471	$916.95	$916.95	$916.90