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	$108.84	13.664%	$123.7119	$123.71	$123.70	$123.70
Purchase #2	$89.99	7.628%	$96.8544	$96.85	$96.85	$96.90
Purchase #3	$217.73	13.253%	$246.5858	$246.59	$246.60	$246.60
Purchase #4	$92.86	6.457%	$98.856	$98.86	$98.85	$98.90
Purchase #5	$201.56	5.427%	$212.4987	$212.50	$212.50	$212.50
Purchase #6	$96.98	3.464%	$100.3394	$100.34	$100.35	$100.30
Purchase #7	$114.40	6.167%	$121.455	$121.46	$121.45	$121.50
7 purchase totals =	$922.36		$1,000.3012	$1,000.31	$1,000.30	$1,000.40