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	$35.51	13.319%	$40.2396	$40.24	$40.25	$40.20
Purchase #2	$36.76	6.785%	$39.2542	$39.25	$39.25	$39.30
Purchase #3	$192.59	12.123%	$215.9377	$215.94	$215.95	$215.90
Purchase #4	$125.48	12.544%	$141.2202	$141.22	$141.20	$141.20
Purchase #5	$87.87	4.470%	$91.7978	$91.80	$91.80	$91.80
Purchase #6	$29.64	13.513%	$33.6453	$33.65	$33.65	$33.60
Purchase #7	$63.56	6.198%	$67.4994	$67.50	$67.50	$67.50
7 purchase totals =	$571.41		$629.5942	$629.60	$629.60	$629.50