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 $87.34   12.445%   $98.2095   $98.21   $98.20   $98.20  
  Purchase #2 $25.91   3.602%   $26.8433   $26.84   $26.85   $26.80  
  Purchase #3 $30.77   9.664%   $33.7436   $33.74   $33.75   $33.70  
  Purchase #4 $130.96   5.522%   $138.1916   $138.19   $138.20   $138.20  
  Purchase #5 $142.91   6.838%   $152.6822   $152.68   $152.70   $152.70  
  Purchase #6 $202.28   6.509%   $215.4464   $215.45   $215.45   $215.40  
  Purchase #7 $246.77   5.721%   $260.8877   $260.89   $260.90   $260.90  
  7 purchase totals = $866.94       $926.0043   $926.00   $926.05   $925.90