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 $242.59   8.673%   $263.6298   $263.63   $263.65   $263.60  
  Purchase #2 $47.27   8.354%   $51.2189   $51.22   $51.20   $51.20  
  Purchase #3 $148.69   4.409%   $155.2457   $155.25   $155.25   $155.20  
  Purchase #4 $247.94   4.151%   $258.232   $258.23   $258.25   $258.20  
  Purchase #5 $76.35   10.637%   $84.4713   $84.47   $84.45   $84.50  
  Purchase #6 $8.70   6.782%   $9.29   $9.29   $9.30   $9.30  
  Purchase #7 $218.88   4.189%   $228.0489   $228.05   $228.05   $228.00  
  7 purchase totals = $990.42       $1,050.1366   $1,050.14   $1,050.15   $1,050.00