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 $111.47   6.712%   $118.9519   $118.95   $118.95   $119.00  
  Purchase #2 $72.72   8.489%   $78.8932   $78.89   $78.90   $78.90  
  Purchase #3 $191.25   12.197%   $214.5768   $214.58   $214.60   $214.60  
  Purchase #4 $65.99   6.617%   $70.3566   $70.36   $70.35   $70.40  
  Purchase #5 $233.68   10.421%   $258.0318   $258.03   $258.05   $258.00  
  Purchase #6 $48.99   6.427%   $52.1386   $52.14   $52.15   $52.10  
  Purchase #7 $220.45   13.456%   $250.1138   $250.11   $250.10   $250.10  
  7 purchase totals = $944.55       $1,043.0627   $1,043.06   $1,043.10   $1,043.10