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 $85.87   10.147%   $94.5832   $94.58   $94.60   $94.60  
  Purchase #2 $217.80   11.567%   $242.9929   $242.99   $243.00   $243.00  
  Purchase #3 $198.93   3.767%   $206.4237   $206.42   $206.40   $206.40  
  Purchase #4 $161.26   8.228%   $174.5285   $174.53   $174.55   $174.50  
  Purchase #5 $53.98   10.475%   $59.6344   $59.63   $59.65   $59.60  
  Purchase #6 $31.25   4.656%   $32.705   $32.71   $32.70   $32.70  
  Purchase #7 $164.79   9.737%   $180.8356   $180.84   $180.85   $180.80  
  7 purchase totals = $913.88       $991.7033   $991.70   $991.75   $991.60