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 $200.26   13.646%   $227.5875   $227.59   $227.60   $227.60  
  Purchase #2 $109.71   8.800%   $119.3645   $119.36   $119.35   $119.40  
  Purchase #3 $73.83   6.380%   $78.5404   $78.54   $78.55   $78.50  
  Purchase #4 $187.65   5.503%   $197.9764   $197.98   $198.00   $198.00  
  Purchase #5 $125.40   8.437%   $135.98   $135.98   $136.00   $136.00  
  Purchase #6 $81.38   10.706%   $90.0925   $90.09   $90.10   $90.10  
  Purchase #7 $220.83   10.817%   $244.7172   $244.72   $244.70   $244.70  
  7 purchase totals = $999.06       $1,094.2585   $1,094.26   $1,094.30   $1,094.30