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	$126.81	7.247%	$135.9999	$136.00	$136.00	$136.00
Purchase #2	$34.39	10.176%	$37.8895	$37.89	$37.90	$37.90
Purchase #3	$123.31	7.405%	$132.4411	$132.44	$132.45	$132.40
Purchase #4	$250.85	12.114%	$281.238	$281.24	$281.25	$281.20
Purchase #5	$40.73	11.669%	$45.4828	$45.48	$45.50	$45.50
Purchase #6	$28.81	7.859%	$31.0742	$31.07	$31.05	$31.10
Purchase #7	$128.63	9.744%	$141.1637	$141.16	$141.15	$141.20
7 purchase totals =	$733.53		$805.2892	$805.28	$805.30	$805.30