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 $49.45   13.302%   $56.0278   $56.03   $56.05   $56.00  
  Purchase #2 $236.55   4.230%   $246.5561   $246.56   $246.55   $246.60  
  Purchase #3 $242.88   7.288%   $260.5811   $260.58   $260.60   $260.60  
  Purchase #4 $226.41   13.709%   $257.4485   $257.45   $257.45   $257.40  
  Purchase #5 $157.82   10.635%   $174.6042   $174.60   $174.60   $174.60  
  Purchase #6 $90.81   3.663%   $94.1364   $94.14   $94.15   $94.10  
  Purchase #7 $111.58   10.824%   $123.6574   $123.66   $123.65   $123.70  
  7 purchase totals = $1,115.50       $1,213.0115   $1,213.02   $1,213.05   $1,213.00