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	$164.45	4.162%	$171.2944	$171.29	$171.30	$171.30
Purchase #2	$70.25	11.566%	$78.3751	$78.38	$78.40	$78.40
Purchase #3	$63.29	9.653%	$69.3994	$69.40	$69.40	$69.40
Purchase #4	$80.46	12.737%	$90.7082	$90.71	$90.70	$90.70
Purchase #5	$155.51	9.641%	$170.5027	$170.50	$170.50	$170.50
Purchase #6	$76.41	5.874%	$80.8983	$80.90	$80.90	$80.90
Purchase #7	$230.47	6.448%	$245.3307	$245.33	$245.35	$245.30
7 purchase totals =	$840.84		$906.5088	$906.51	$906.55	$906.50