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	$33.50	11.515%	$37.3575	$37.36	$37.35	$37.40
Purchase #2	$78.88	5.234%	$83.0086	$83.01	$83.00	$83.00
Purchase #3	$98.68	12.329%	$110.8463	$110.85	$110.85	$110.80
Purchase #4	$89.33	3.173%	$92.1644	$92.16	$92.15	$92.20
Purchase #5	$107.44	13.783%	$122.2485	$122.25	$122.25	$122.20
Purchase #6	$39.90	6.782%	$42.606	$42.61	$42.60	$42.60
Purchase #7	$67.81	12.796%	$76.487	$76.49	$76.50	$76.50
7 purchase totals =	$515.54		$564.7183	$564.73	$564.70	$564.70