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 $50.42   11.519%   $56.2279   $56.23   $56.25   $56.20  
  Purchase #2 $109.84   6.192%   $116.6413   $116.64   $116.65   $116.60  
  Purchase #3 $68.81   8.863%   $74.9086   $74.91   $74.90   $74.90  
  Purchase #4 $118.72   11.584%   $132.4725   $132.47   $132.45   $132.50  
  Purchase #5 $211.29   12.464%   $237.6252   $237.63   $237.65   $237.60  
  Purchase #6 $242.58   8.304%   $262.7238   $262.72   $262.70   $262.70  
  Purchase #7 $134.90   6.822%   $144.1029   $144.10   $144.10   $144.10  
  7 purchase totals = $936.56       $1,024.7022   $1,024.70   $1,024.70   $1,024.60