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 $57.78   6.653%   $61.6241   $61.62   $61.60   $61.60  
  Purchase #2 $50.60   13.298%   $57.3288   $57.33   $57.35   $57.30  
  Purchase #3 $242.32   7.296%   $259.9997   $260.00   $260.00   $260.00  
  Purchase #4 $236.47   9.439%   $258.7904   $258.79   $258.80   $258.80  
  Purchase #5 $175.49   10.445%   $193.8199   $193.82   $193.80   $193.80  
  Purchase #6 $186.65   12.586%   $210.1418   $210.14   $210.15   $210.10  
  Purchase #7 $53.73   12.141%   $60.2534   $60.25   $60.25   $60.30  
  7 purchase totals = $1,003.04       $1,101.9581   $1,101.95   $1,101.95   $1,101.90