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 $62.48   7.849%   $67.3841   $67.38   $67.40   $67.40  
  Purchase #2 $242.96   7.661%   $261.5732   $261.57   $261.55   $261.60  
  Purchase #3 $115.25   9.212%   $125.8668   $125.87   $125.85   $125.90  
  Purchase #4 $191.29   12.292%   $214.8034   $214.80   $214.80   $214.80  
  Purchase #5 $30.34   11.794%   $33.9183   $33.92   $33.90   $33.90  
  Purchase #6 $242.81   10.190%   $267.5523   $267.55   $267.55   $267.60  
  Purchase #7 $34.55   12.819%   $38.979   $38.98   $39.00   $39.00  
  7 purchase totals = $919.68       $1,010.0771   $1,010.07   $1,010.05   $1,010.20