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	$155.69	3.589%	$161.2777	$161.28	$161.30	$161.30
Purchase #2	$21.41	11.571%	$23.8874	$23.89	$23.90	$23.90
Purchase #3	$196.76	6.226%	$209.0103	$209.01	$209.00	$209.00
Purchase #4	$164.84	9.252%	$180.091	$180.09	$180.10	$180.10
Purchase #5	$12.66	7.491%	$13.6084	$13.61	$13.60	$13.60
Purchase #6	$133.85	6.640%	$142.7376	$142.74	$142.75	$142.70
Purchase #7	$85.34	5.735%	$90.2342	$90.23	$90.25	$90.20
7 purchase totals =	$770.55		$820.8466	$820.85	$820.90	$820.80