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 $141.65   11.539%   $157.995   $158.00   $158.00   $158.00  
  Purchase #2 $123.92   11.857%   $138.6132   $138.61   $138.60   $138.60  
  Purchase #3 $208.90   8.619%   $226.9051   $226.91   $226.90   $226.90  
  Purchase #4 $82.39   10.571%   $91.0994   $91.10   $91.10   $91.10  
  Purchase #5 $50.31   12.544%   $56.6209   $56.62   $56.60   $56.60  
  Purchase #6 $42.81   11.767%   $47.8475   $47.85   $47.85   $47.80  
  Purchase #7 $232.76   13.233%   $263.5611   $263.56   $263.55   $263.60  
  7 purchase totals = $882.74       $982.6422   $982.65   $982.60   $982.60