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	$136.93	13.200%	$155.0048	$155.00	$155.00	$155.00
Purchase #2	$155.31	9.105%	$169.451	$169.45	$169.45	$169.50
Purchase #3	$119.51	6.707%	$127.5255	$127.53	$127.55	$127.50
Purchase #4	$199.63	8.664%	$216.9259	$216.93	$216.95	$216.90
Purchase #5	$124.45	5.470%	$131.2574	$131.26	$131.25	$131.30
Purchase #6	$134.96	3.739%	$140.0062	$140.01	$140.00	$140.00
Purchase #7	$242.65	13.574%	$275.5873	$275.59	$275.60	$275.60
7 purchase totals =	$1,113.44		$1,215.7581	$1,215.77	$1,215.80	$1,215.80