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 $91.91   5.279%   $96.7619   $96.76   $96.75   $96.80  
  Purchase #2 $123.37   8.677%   $134.0748   $134.07   $134.05   $134.10  
  Purchase #3 $128.80   12.367%   $144.7287   $144.73   $144.75   $144.70  
  Purchase #4 $94.51   9.253%   $103.255   $103.26   $103.25   $103.30  
  Purchase #5 $208.42   6.850%   $222.6968   $222.70   $222.70   $222.70  
  Purchase #6 $115.39   6.272%   $122.6273   $122.63   $122.65   $122.60  
  Purchase #7 $24.62   11.500%   $27.4513   $27.45   $27.45   $27.50  
  7 purchase totals = $787.02       $851.5958   $851.60   $851.60   $851.70