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 $201.75   3.439%   $208.6882   $208.69   $208.70   $208.70  
  Purchase #2 $40.42   13.415%   $45.8423   $45.84   $45.85   $45.80  
  Purchase #3 $18.56   4.666%   $19.426   $19.43   $19.45   $19.40  
  Purchase #4 $157.31   11.523%   $175.4368   $175.44   $175.45   $175.40  
  Purchase #5 $237.60   9.759%   $260.7874   $260.79   $260.80   $260.80  
  Purchase #6 $24.66   3.175%   $25.443   $25.44   $25.45   $25.40  
  Purchase #7 $43.86   9.292%   $47.9355   $47.94   $47.95   $47.90  
  7 purchase totals = $724.16       $783.5592   $783.57   $783.65   $783.40