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	$58.91	13.314%	$66.7533	$66.75	$66.75	$66.80
Purchase #2	$92.90	7.652%	$100.0087	$100.01	$100.00	$100.00
Purchase #3	$29.29	8.765%	$31.8573	$31.86	$31.85	$31.90
Purchase #4	$184.86	6.755%	$197.3473	$197.35	$197.35	$197.30
Purchase #5	$146.41	8.723%	$159.1813	$159.18	$159.20	$159.20
Purchase #6	$184.71	8.540%	$200.4842	$200.48	$200.50	$200.50
Purchase #7	$102.44	9.282%	$111.9485	$111.95	$111.95	$111.90
7 purchase totals =	$799.52		$867.5806	$867.58	$867.60	$867.60