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	$35.92	12.471%	$40.3996	$40.40	$40.40	$40.40
Purchase #2	$146.40	3.559%	$151.6104	$151.61	$151.60	$151.60
Purchase #3	$58.96	9.394%	$64.4987	$64.50	$64.50	$64.50
Purchase #4	$170.78	13.721%	$194.2127	$194.21	$194.20	$194.20
Purchase #5	$50.66	7.868%	$54.6459	$54.65	$54.65	$54.60
Purchase #6	$78.78	9.267%	$86.0805	$86.08	$86.10	$86.10
Purchase #7	$25.48	11.789%	$28.4838	$28.48	$28.50	$28.50
7 purchase totals =	$566.98		$619.9316	$619.93	$619.95	$619.90