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	$172.91	7.602%	$186.0546	$186.05	$186.05	$186.10
Purchase #2	$170.81	9.292%	$186.6817	$186.68	$186.70	$186.70
Purchase #3	$82.85	10.840%	$91.8309	$91.83	$91.85	$91.80
Purchase #4	$156.91	7.393%	$168.5104	$168.51	$168.50	$168.50
Purchase #5	$236.56	10.712%	$261.9003	$261.90	$261.90	$261.90
Purchase #6	$73.96	13.330%	$83.8189	$83.82	$83.80	$83.80
Purchase #7	$224.80	13.796%	$255.8134	$255.81	$255.80	$255.80
7 purchase totals =	$1,118.80		$1,234.6102	$1,234.60	$1,234.60	$1,234.60