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	$134.39	5.572%	$141.8782	$141.88	$141.90	$141.90
Purchase #2	$211.69	9.134%	$231.0258	$231.03	$231.05	$231.00
Purchase #3	$104.38	6.351%	$111.0092	$111.01	$111.00	$111.00
Purchase #4	$15.61	7.684%	$16.8095	$16.81	$16.80	$16.80
Purchase #5	$100.67	8.582%	$109.3095	$109.31	$109.30	$109.30
Purchase #6	$137.68	3.404%	$142.3666	$142.37	$142.35	$142.40
Purchase #7	$42.43	4.811%	$44.4713	$44.47	$44.45	$44.50
7 purchase totals =	$746.85		$796.8701	$796.88	$796.85	$796.90