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 $182.87   13.472%   $207.5062   $207.51   $207.50   $207.50  
  Purchase #2 $25.68   4.477%   $26.8297   $26.83   $26.85   $26.80  
  Purchase #3 $178.53   8.205%   $193.1784   $193.18   $193.20   $193.20  
  Purchase #4 $119.36   5.844%   $126.3354   $126.34   $126.35   $126.30  
  Purchase #5 $190.99   13.527%   $216.8252   $216.83   $216.85   $216.80  
  Purchase #6 $75.92   8.718%   $82.5387   $82.54   $82.55   $82.50  
  Purchase #7 $134.66   5.726%   $142.3706   $142.37   $142.35   $142.40  
  7 purchase totals = $908.01       $995.5842   $995.60   $995.65   $995.50