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	$111.84	6.611%	$119.2337	$119.23	$119.25	$119.20
Purchase #2	$45.25	13.709%	$51.4533	$51.45	$51.45	$51.50
Purchase #3	$223.49	12.106%	$250.5457	$250.55	$250.55	$250.50
Purchase #4	$27.25	10.645%	$30.1508	$30.15	$30.15	$30.20
Purchase #5	$40.59	5.256%	$42.7234	$42.72	$42.70	$42.70
Purchase #6	$127.45	6.853%	$136.1841	$136.18	$136.20	$136.20
Purchase #7	$84.55	6.783%	$90.285	$90.29	$90.30	$90.30
7 purchase totals =	$660.42		$720.5760	$720.57	$720.60	$720.60