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 $93.75   4.622%   $98.0831   $98.08   $98.10   $98.10  
  Purchase #2 $84.62   12.786%   $95.4395   $95.44   $95.45   $95.40  
  Purchase #3 $119.89   5.422%   $126.3904   $126.39   $126.40   $126.40  
  Purchase #4 $200.25   11.713%   $223.7053   $223.71   $223.70   $223.70  
  Purchase #5 $113.64   7.191%   $121.8119   $121.81   $121.80   $121.80  
  Purchase #6 $6.82   11.437%   $7.6   $7.60   $7.60   $7.60  
  Purchase #7 $23.34   3.597%   $24.1795   $24.18   $24.20   $24.20  
  7 purchase totals = $642.31       $697.2097   $697.21   $697.25   $697.20