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 $239.27   13.117%   $270.655   $270.66   $270.65   $270.70  
  Purchase #2 $119.30   12.395%   $134.0872   $134.09   $134.10   $134.10  
  Purchase #3 $214.98   12.867%   $242.6415   $242.64   $242.65   $242.60  
  Purchase #4 $105.69   6.799%   $112.8759   $112.88   $112.90   $112.90  
  Purchase #5 $119.29   5.192%   $125.4835   $125.48   $125.50   $125.50  
  Purchase #6 $29.87   13.440%   $33.8845   $33.88   $33.90   $33.90  
  Purchase #7 $95.61   9.320%   $104.5209   $104.52   $104.50   $104.50  
  7 purchase totals = $924.01       $1,024.1485   $1,024.15   $1,024.20   $1,024.20