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	$28.28	10.260%	$31.1815	$31.18	$31.20	$31.20
Purchase #2	$35.83	3.514%	$37.0891	$37.09	$37.10	$37.10
Purchase #3	$109.55	12.745%	$123.5121	$123.51	$123.50	$123.50
Purchase #4	$204.43	10.252%	$225.3882	$225.39	$225.40	$225.40
Purchase #5	$187.78	11.504%	$209.3822	$209.38	$209.40	$209.40
Purchase #6	$34.38	8.207%	$37.2016	$37.20	$37.20	$37.20
Purchase #7	$250.70	13.409%	$284.3164	$284.32	$284.30	$284.30
7 purchase totals =	$850.95		$948.0711	$948.07	$948.10	$948.10