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 $182.66   12.642%   $205.7519   $205.75   $205.75   $205.80  
  Purchase #2 $121.57   10.824%   $134.7287   $134.73   $134.75   $134.70  
  Purchase #3 $200.37   13.535%   $227.4901   $227.49   $227.50   $227.50  
  Purchase #4 $77.96   3.369%   $80.5865   $80.59   $80.60   $80.60  
  Purchase #5 $57.74   5.161%   $60.72   $60.72   $60.70   $60.70  
  Purchase #6 $16.40   4.446%   $17.1291   $17.13   $17.15   $17.10  
  Purchase #7 $111.46   3.358%   $115.2028   $115.20   $115.20   $115.20  
  7 purchase totals = $768.16       $841.6091   $841.61   $841.65   $841.60