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	$187.96	10.296%	$207.3124	$207.31	$207.30	$207.30
Purchase #2	$157.94	13.630%	$179.4672	$179.47	$179.45	$179.50
Purchase #3	$198.64	8.497%	$215.5184	$215.52	$215.50	$215.50
Purchase #4	$226.90	4.385%	$236.8496	$236.85	$236.85	$236.80
Purchase #5	$107.61	11.347%	$119.8205	$119.82	$119.80	$119.80
Purchase #6	$37.91	12.837%	$42.7765	$42.78	$42.80	$42.80
Purchase #7	$33.50	10.128%	$36.8929	$36.89	$36.90	$36.90
7 purchase totals =	$950.46		$1,038.6375	$1,038.64	$1,038.60	$1,038.60