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	$123.47	10.641%	$136.6084	$136.61	$136.60	$136.60
Purchase #2	$122.47	3.302%	$126.514	$126.51	$126.50	$126.50
Purchase #3	$142.46	9.712%	$156.2957	$156.30	$156.30	$156.30
Purchase #4	$6.53	13.469%	$7.4095	$7.41	$7.40	$7.40
Purchase #5	$231.51	12.863%	$261.2891	$261.29	$261.30	$261.30
Purchase #6	$153.90	12.816%	$173.6238	$173.62	$173.60	$173.60
Purchase #7	$19.61	11.314%	$21.8287	$21.83	$21.85	$21.80
7 purchase totals =	$799.95		$883.5692	$883.57	$883.55	$883.50