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	$94.48	7.233%	$101.3137	$101.31	$101.30	$101.30
Purchase #2	$112.75	5.841%	$119.3357	$119.34	$119.35	$119.30
Purchase #3	$245.29	11.871%	$274.4084	$274.41	$274.40	$274.40
Purchase #4	$73.58	6.741%	$78.54	$78.54	$78.55	$78.50
Purchase #5	$43.64	11.836%	$48.8052	$48.81	$48.80	$48.80
Purchase #6	$52.37	4.282%	$54.6125	$54.61	$54.60	$54.60
Purchase #7	$143.81	12.440%	$161.7	$161.70	$161.70	$161.70
7 purchase totals =	$765.92		$838.7155	$838.72	$838.70	$838.60