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 $24.80   4.851%   $26.003   $26.00   $26.00   $26.00  
  Purchase #2 $66.80   10.369%   $73.7265   $73.73   $73.75   $73.70  
  Purchase #3 $146.54   4.235%   $152.746   $152.75   $152.75   $152.70  
  Purchase #4 $159.70   4.801%   $167.3672   $167.37   $167.35   $167.40  
  Purchase #5 $206.50   7.732%   $222.4666   $222.47   $222.45   $222.50  
  Purchase #6 $178.87   5.526%   $188.7544   $188.75   $188.75   $188.80  
  Purchase #7 $100.97   3.777%   $104.7836   $104.78   $104.80   $104.80  
  7 purchase totals = $884.18       $935.8473   $935.85   $935.85   $935.90