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	$33.65	12.343%	$37.8034	$37.80	$37.80	$37.80
Purchase #2	$187.37	11.189%	$208.3348	$208.33	$208.35	$208.30
Purchase #3	$181.37	10.179%	$199.8317	$199.83	$199.85	$199.80
Purchase #4	$132.58	7.750%	$142.855	$142.86	$142.85	$142.90
Purchase #5	$121.35	8.651%	$131.848	$131.85	$131.85	$131.80
Purchase #6	$197.73	12.473%	$222.3929	$222.39	$222.40	$222.40
Purchase #7	$237.68	10.589%	$262.8479	$262.85	$262.85	$262.80
7 purchase totals =	$1,091.73		$1,205.9137	$1,205.91	$1,205.95	$1,205.80