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 $94.25   4.166%   $98.1765   $98.18   $98.20   $98.20  
  Purchase #2 $182.90   11.791%   $204.4657   $204.47   $204.45   $204.50  
  Purchase #3 $147.31   11.794%   $164.6837   $164.68   $164.70   $164.70  
  Purchase #4 $129.62   5.226%   $136.3939   $136.39   $136.40   $136.40  
  Purchase #5 $32.29   10.617%   $35.7182   $35.72   $35.70   $35.70  
  Purchase #6 $72.95   5.263%   $76.7894   $76.79   $76.80   $76.80  
  Purchase #7 $99.49   7.204%   $106.6573   $106.66   $106.65   $106.70  
  7 purchase totals = $758.81       $822.8847   $822.89   $822.90   $823.00