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 $113.76   5.319%   $119.8109   $119.81   $119.80   $119.80  
  Purchase #2 $52.58   12.158%   $58.9727   $58.97   $58.95   $59.00  
  Purchase #3 $23.90   11.594%   $26.671   $26.67   $26.65   $26.70  
  Purchase #4 $130.87   3.157%   $135.0016   $135.00   $135.00   $135.00  
  Purchase #5 $22.66   13.858%   $25.8002   $25.80   $25.80   $25.80  
  Purchase #6 $232.91   12.738%   $262.5781   $262.58   $262.60   $262.60  
  Purchase #7 $242.26   3.633%   $251.0613   $251.06   $251.05   $251.10  
  7 purchase totals = $818.94       $879.8958   $879.89   $879.85   $880.00