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 $239.42   9.291%   $261.6645   $261.66   $261.65   $261.70  
  Purchase #2 $250.38   9.564%   $274.3263   $274.33   $274.35   $274.30  
  Purchase #3 $55.68   6.708%   $59.415   $59.42   $59.40   $59.40  
  Purchase #4 $89.55   12.237%   $100.5082   $100.51   $100.50   $100.50  
  Purchase #5 $122.79   13.178%   $138.9713   $138.97   $138.95   $139.00  
  Purchase #6 $194.30   10.342%   $214.3945   $214.39   $214.40   $214.40  
  Purchase #7 $60.32   6.351%   $64.1509   $64.15   $64.15   $64.20  
  7 purchase totals = $1,012.44       $1,113.4307   $1,113.43   $1,113.40   $1,113.50