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	$40.27	4.781%	$42.1953	$42.20	$42.20	$42.20
Purchase #2	$74.43	5.610%	$78.6055	$78.61	$78.60	$78.60
Purchase #3	$39.95	12.794%	$45.0612	$45.06	$45.05	$45.10
Purchase #4	$90.94	13.233%	$102.9741	$102.97	$102.95	$103.00
Purchase #5	$106.56	5.403%	$112.3174	$112.32	$112.30	$112.30
Purchase #6	$246.96	9.605%	$270.6805	$270.68	$270.70	$270.70
Purchase #7	$179.66	7.863%	$193.7867	$193.79	$193.80	$193.80
7 purchase totals =	$778.77		$845.6207	$845.63	$845.60	$845.70