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	$172.87	5.521%	$182.4142	$182.41	$182.40	$182.40
Purchase #2	$89.37	12.242%	$100.3107	$100.31	$100.30	$100.30
Purchase #3	$169.25	8.372%	$183.4196	$183.42	$183.40	$183.40
Purchase #4	$87.50	7.217%	$93.8149	$93.81	$93.80	$93.80
Purchase #5	$34.80	3.139%	$35.8924	$35.89	$35.90	$35.90
Purchase #6	$96.96	4.329%	$101.1574	$101.16	$101.15	$101.20
Purchase #7	$17.27	7.712%	$18.6019	$18.60	$18.60	$18.60
7 purchase totals =	$668.02		$715.6111	$715.60	$715.55	$715.60