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	$90.49	13.261%	$102.4899	$102.49	$102.50	$102.50
Purchase #2	$15.85	7.513%	$17.0408	$17.04	$17.05	$17.00
Purchase #3	$78.38	13.448%	$88.9205	$88.92	$88.90	$88.90
Purchase #4	$37.82	12.166%	$42.4212	$42.42	$42.40	$42.40
Purchase #5	$11.74	9.127%	$12.8115	$12.81	$12.80	$12.80
Purchase #6	$33.48	6.153%	$35.54	$35.54	$35.55	$35.50
Purchase #7	$18.85	5.535%	$19.8933	$19.89	$19.90	$19.90
7 purchase totals =	$286.61		$319.1172	$319.11	$319.10	$319.00