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 $93.91   10.759%   $104.0138   $104.01   $104.00   $104.00  
  Purchase #2 $168.41   3.854%   $174.9005   $174.90   $174.90   $174.90  
  Purchase #3 $43.49   9.565%   $47.6498   $47.65   $47.65   $47.60  
  Purchase #4 $249.72   3.710%   $258.9846   $258.98   $259.00   $259.00  
  Purchase #5 $26.90   11.512%   $29.9967   $30.00   $30.00   $30.00  
  Purchase #6 $146.73   8.375%   $159.0186   $159.02   $159.00   $159.00  
  Purchase #7 $235.59   6.497%   $250.8963   $250.90   $250.90   $250.90  
  7 purchase totals = $964.75       $1,025.4603   $1,025.46   $1,025.45   $1,025.40