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 $55.38   5.538%   $58.4469   $58.45   $58.45   $58.40  
  Purchase #2 $71.29   7.399%   $76.5647   $76.56   $76.55   $76.60  
  Purchase #3 $170.62   12.233%   $191.4919   $191.49   $191.50   $191.50  
  Purchase #4 $213.51   6.813%   $228.0564   $228.06   $228.05   $228.10  
  Purchase #5 $225.97   9.189%   $246.7344   $246.73   $246.75   $246.70  
  Purchase #6 $56.96   10.255%   $62.8012   $62.80   $62.80   $62.80  
  Purchase #7 $32.93   5.763%   $34.8278   $34.83   $34.85   $34.80  
  7 purchase totals = $826.66       $898.9233   $898.92   $898.95   $898.90