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	8.320%	$38.9085	$38.91	$38.90	$38.90
Purchase #2	$144.89	12.699%	$163.2896	$163.29	$163.30	$163.30
Purchase #3	$96.89	3.827%	$100.598	$100.60	$100.60	$100.60
Purchase #4	$113.85	5.305%	$119.8897	$119.89	$119.90	$119.90
Purchase #5	$214.85	6.140%	$228.0418	$228.04	$228.05	$228.00
Purchase #6	$162.55	7.241%	$174.3202	$174.32	$174.30	$174.30
Purchase #7	$227.74	12.477%	$256.1551	$256.16	$256.15	$256.20
7 purchase totals =	$996.69		$1,081.2029	$1,081.21	$1,081.20	$1,081.20