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	$26.87	9.533%	$29.4315	$29.43	$29.45	$29.40
Purchase #2	$125.31	13.701%	$142.4787	$142.48	$142.50	$142.50
Purchase #3	$224.84	11.323%	$250.2986	$250.30	$250.30	$250.30
Purchase #4	$32.51	7.333%	$34.894	$34.89	$34.90	$34.90
Purchase #5	$37.72	12.472%	$42.4244	$42.42	$42.40	$42.40
Purchase #6	$39.91	8.409%	$43.266	$43.27	$43.25	$43.30
Purchase #7	$158.72	9.864%	$174.3761	$174.38	$174.40	$174.40
7 purchase totals =	$645.88		$717.1693	$717.17	$717.20	$717.20