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	$186.68	12.778%	$210.534	$210.53	$210.55	$210.50
Purchase #2	$91.86	11.329%	$102.2668	$102.27	$102.25	$102.30
Purchase #3	$213.38	6.677%	$227.6274	$227.63	$227.65	$227.60
Purchase #4	$233.38	9.502%	$255.5558	$255.56	$255.55	$255.60
Purchase #5	$31.55	4.292%	$32.9041	$32.90	$32.90	$32.90
Purchase #6	$51.92	13.721%	$59.0439	$59.04	$59.05	$59.00
Purchase #7	$80.60	8.227%	$87.231	$87.23	$87.25	$87.20
7 purchase totals =	$889.37		$975.1630	$975.16	$975.20	$975.10