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	$36.93	8.699%	$40.1425	$40.14	$40.15	$40.10
Purchase #2	$64.61	3.630%	$66.9553	$66.96	$66.95	$67.00
Purchase #3	$72.46	6.243%	$76.9837	$76.98	$77.00	$77.00
Purchase #4	$188.33	11.775%	$210.5059	$210.51	$210.50	$210.50
Purchase #5	$190.36	4.482%	$198.8919	$198.89	$198.90	$198.90
Purchase #6	$50.90	12.775%	$57.4025	$57.40	$57.40	$57.40
Purchase #7	$38.59	10.339%	$42.5798	$42.58	$42.60	$42.60
7 purchase totals =	$642.18		$693.4616	$693.46	$693.50	$693.50