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 $47.36   8.799%   $51.5272   $51.53   $51.55   $51.50  
  Purchase #2 $199.71   6.530%   $212.7511   $212.75   $212.75   $212.80  
  Purchase #3 $122.73   10.728%   $135.8965   $135.90   $135.90   $135.90  
  Purchase #4 $168.76   5.413%   $177.895   $177.90   $177.90   $177.90  
  Purchase #5 $29.29   3.298%   $30.256   $30.26   $30.25   $30.30  
  Purchase #6 $247.46   3.870%   $257.0367   $257.04   $257.05   $257.00  
  Purchase #7 $141.53   12.778%   $159.6147   $159.61   $159.60   $159.60  
  7 purchase totals = $956.84       $1,024.9772   $1,024.99   $1,025.00   $1,025.00