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 $118.94   6.289%   $126.4201   $126.42   $126.40   $126.40  
  Purchase #2 $203.69   6.165%   $216.2475   $216.25   $216.25   $216.20  
  Purchase #3 $56.32   11.554%   $62.8272   $62.83   $62.85   $62.80  
  Purchase #4 $115.79   5.839%   $122.551   $122.55   $122.55   $122.60  
  Purchase #5 $207.86   13.483%   $235.8858   $235.89   $235.90   $235.90  
  Purchase #6 $172.34   5.591%   $181.9755   $181.98   $182.00   $182.00  
  Purchase #7 $25.68   3.400%   $26.5531   $26.55   $26.55   $26.60  
  7 purchase totals = $900.62       $972.4602   $972.47   $972.50   $972.50