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 $135.86   5.845%   $143.801   $143.80   $143.80   $143.80  
  Purchase #2 $67.60   13.290%   $76.584   $76.58   $76.60   $76.60  
  Purchase #3 $207.40   13.264%   $234.9095   $234.91   $234.90   $234.90  
  Purchase #4 $115.41   13.225%   $130.673   $130.67   $130.65   $130.70  
  Purchase #5 $82.73   5.372%   $87.1743   $87.17   $87.15   $87.20  
  Purchase #6 $58.72   3.452%   $60.747   $60.75   $60.75   $60.70  
  Purchase #7 $121.66   4.259%   $126.8415   $126.84   $126.85   $126.80  
  7 purchase totals = $789.38       $860.7303   $860.72   $860.70   $860.70