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 $86.81   13.663%   $98.6709   $98.67   $98.65   $98.70  
  Purchase #2 $26.92   7.387%   $28.9086   $28.91   $28.90   $28.90  
  Purchase #3 $116.67   8.797%   $126.9335   $126.93   $126.95   $126.90  
  Purchase #4 $153.50   8.152%   $166.0133   $166.01   $166.00   $166.00  
  Purchase #5 $191.41   10.755%   $211.9961   $212.00   $212.00   $212.00  
  Purchase #6 $190.43   9.486%   $208.4942   $208.49   $208.50   $208.50  
  Purchase #7 $193.87   7.108%   $207.6503   $207.65   $207.65   $207.70  
  7 purchase totals = $959.61       $1,048.6669   $1,048.66   $1,048.65   $1,048.70