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 $41.95   7.143%   $44.9465   $44.95   $44.95   $44.90  
  Purchase #2 $79.53   4.333%   $82.976   $82.98   $83.00   $83.00  
  Purchase #3 $217.28   9.535%   $237.9976   $238.00   $238.00   $238.00  
  Purchase #4 $220.32   5.549%   $232.5456   $232.55   $232.55   $232.50  
  Purchase #5 $158.95   5.736%   $168.0674   $168.07   $168.05   $168.10  
  Purchase #6 $144.30   8.504%   $156.5713   $156.57   $156.55   $156.60  
  Purchase #7 $121.38   12.712%   $136.8098   $136.81   $136.80   $136.80  
  7 purchase totals = $983.71       $1,059.9142   $1,059.93   $1,059.90   $1,059.90