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 $63.60   7.764%   $68.5379   $68.54   $68.55   $68.50  
  Purchase #2 $232.29   4.346%   $242.3853   $242.39   $242.40   $242.40  
  Purchase #3 $166.33   12.845%   $187.6951   $187.70   $187.70   $187.70  
  Purchase #4 $247.27   4.326%   $257.9669   $257.97   $257.95   $258.00  
  Purchase #5 $85.25   6.224%   $90.556   $90.56   $90.55   $90.60  
  Purchase #6 $187.58   5.392%   $197.6943   $197.69   $197.70   $197.70  
  Purchase #7 $126.56   6.783%   $135.1446   $135.14   $135.15   $135.10  
  7 purchase totals = $1,108.88       $1,179.9801   $1,179.99   $1,180.00   $1,180.00