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 $17.86   7.565%   $19.2111   $19.21   $19.20   $19.20  
  Purchase #2 $103.78   8.439%   $112.538   $112.54   $112.55   $112.50  
  Purchase #3 $23.57   12.812%   $26.5898   $26.59   $26.60   $26.60  
  Purchase #4 $168.71   6.239%   $179.2358   $179.24   $179.25   $179.20  
  Purchase #5 $177.48   7.542%   $190.8655   $190.87   $190.85   $190.90  
  Purchase #6 $241.78   7.699%   $260.3946   $260.39   $260.40   $260.40  
  Purchase #7 $207.49   13.390%   $235.2729   $235.27   $235.25   $235.30  
  7 purchase totals = $940.67       $1,024.1077   $1,024.11   $1,024.10   $1,024.10