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 $52.49   5.277%   $55.2599   $55.26   $55.25   $55.30  
  Purchase #2 $195.31   10.675%   $216.1593   $216.16   $216.15   $216.20  
  Purchase #3 $189.54   8.202%   $205.0861   $205.09   $205.10   $205.10  
  Purchase #4 $152.56   6.211%   $162.0355   $162.04   $162.05   $162.00  
  Purchase #5 $37.27   6.319%   $39.6251   $39.63   $39.65   $39.60  
  Purchase #6 $161.51   13.811%   $183.8161   $183.82   $183.80   $183.80  
  Purchase #7 $27.27   12.267%   $30.6152   $30.62   $30.60   $30.60  
  7 purchase totals = $815.95       $892.5972   $892.62   $892.60   $892.60