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 $240.45   6.464%   $255.9927   $255.99   $256.00   $256.00  
  Purchase #2 $66.47   4.119%   $69.2079   $69.21   $69.20   $69.20  
  Purchase #3 $48.78   13.641%   $55.4341   $55.43   $55.45   $55.40  
  Purchase #4 $39.59   4.737%   $41.4654   $41.47   $41.45   $41.50  
  Purchase #5 $146.66   13.152%   $165.9487   $165.95   $165.95   $165.90  
  Purchase #6 $165.88   6.233%   $176.2193   $176.22   $176.20   $176.20  
  Purchase #7 $241.98   8.429%   $262.3765   $262.38   $262.40   $262.40  
  7 purchase totals = $949.81       $1,026.6446   $1,026.65   $1,026.65   $1,026.60