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 $8.59   11.614%   $9.5876   $9.59   $9.60   $9.60  
  Purchase #2 $20.65   10.859%   $22.8924   $22.89   $22.90   $22.90  
  Purchase #3 $115.44   7.225%   $123.7805   $123.78   $123.80   $123.80  
  Purchase #4 $174.66   9.350%   $190.9907   $190.99   $191.00   $191.00  
  Purchase #5 $103.81   6.122%   $110.1652   $110.17   $110.15   $110.20  
  Purchase #6 $223.58   6.778%   $238.7343   $238.73   $238.75   $238.70  
  Purchase #7 $54.76   8.652%   $59.4978   $59.50   $59.50   $59.50  
  7 purchase totals = $701.49       $755.6485   $755.65   $755.70   $755.70