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	$76.64	7.531%	$82.4118	$82.41	$82.40	$82.40
Purchase #2	$34.36	3.602%	$35.5976	$35.60	$35.60	$35.60
Purchase #3	$230.33	8.446%	$249.7837	$249.78	$249.80	$249.80
Purchase #4	$63.95	12.434%	$71.9015	$71.90	$71.90	$71.90
Purchase #5	$32.79	13.866%	$37.3367	$37.34	$37.35	$37.30
Purchase #6	$231.52	12.663%	$260.8374	$260.84	$260.85	$260.80
Purchase #7	$134.53	11.837%	$150.4543	$150.45	$150.45	$150.50
7 purchase totals =	$804.12		$888.3230	$888.32	$888.35	$888.30