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 $91.79   12.787%   $103.5272   $103.53   $103.55   $103.50  
  Purchase #2 $136.26   13.590%   $154.7777   $154.78   $154.80   $154.80  
  Purchase #3 $104.57   12.552%   $117.6956   $117.70   $117.70   $117.70  
  Purchase #4 $31.79   9.608%   $34.8444   $34.84   $34.85   $34.80  
  Purchase #5 $165.30   5.629%   $174.6047   $174.60   $174.60   $174.60  
  Purchase #6 $86.89   8.254%   $94.0619   $94.06   $94.05   $94.10  
  Purchase #7 $105.94   12.691%   $119.3848   $119.38   $119.40   $119.40  
  7 purchase totals = $722.54       $798.8963   $798.89   $798.95   $798.90