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 $200.76   13.402%   $227.6659   $227.67   $227.65   $227.70  
  Purchase #2 $81.74   11.239%   $90.9268   $90.93   $90.95   $90.90  
  Purchase #3 $77.42   10.682%   $85.69   $85.69   $85.70   $85.70  
  Purchase #4 $151.93   8.729%   $165.192   $165.19   $165.20   $165.20  
  Purchase #5 $140.30   10.646%   $155.2363   $155.24   $155.25   $155.20  
  Purchase #6 $108.93   11.640%   $121.6095   $121.61   $121.60   $121.60  
  Purchase #7 $139.98   7.372%   $150.2993   $150.30   $150.30   $150.30  
  7 purchase totals = $901.06       $996.6198   $996.63   $996.65   $996.60