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	$213.39	5.256%	$224.6058	$224.61	$224.60	$224.60
Purchase #2	$131.97	8.150%	$142.7256	$142.73	$142.75	$142.70
Purchase #3	$150.61	4.533%	$157.4372	$157.44	$157.45	$157.40
Purchase #4	$116.49	6.306%	$123.8359	$123.84	$123.85	$123.80
Purchase #5	$127.88	10.586%	$141.4174	$141.42	$141.40	$141.40
Purchase #6	$30.35	3.764%	$31.4924	$31.49	$31.50	$31.50
Purchase #7	$19.80	8.788%	$21.54	$21.54	$21.55	$21.50
7 purchase totals =	$790.49		$843.0543	$843.07	$843.10	$842.90