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	$122.29	9.800%	$134.2744	$134.27	$134.25	$134.30
Purchase #2	$139.29	3.505%	$144.1721	$144.17	$144.15	$144.20
Purchase #3	$95.31	11.710%	$106.4708	$106.47	$106.45	$106.50
Purchase #4	$10.42	4.318%	$10.8699	$10.87	$10.85	$10.90
Purchase #5	$30.47	4.494%	$31.8393	$31.84	$31.85	$31.80
Purchase #6	$209.29	8.741%	$227.584	$227.58	$227.60	$227.60
Purchase #7	$121.57	8.290%	$131.6482	$131.65	$131.65	$131.60
7 purchase totals =	$728.64		$786.8587	$786.85	$786.80	$786.90