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 $56.58   8.258%   $61.2524   $61.25   $61.25   $61.30  
  Purchase #2 $60.47   11.587%   $67.4767   $67.48   $67.50   $67.50  
  Purchase #3 $171.77   3.419%   $177.6428   $177.64   $177.65   $177.60  
  Purchase #4 $82.63   4.388%   $86.2558   $86.26   $86.25   $86.30  
  Purchase #5 $181.45   4.528%   $189.6661   $189.67   $189.65   $189.70  
  Purchase #6 $126.81   8.441%   $137.514   $137.51   $137.50   $137.50  
  Purchase #7 $46.82   8.818%   $50.9486   $50.95   $50.95   $50.90  
  7 purchase totals = $726.53       $770.7564   $770.76   $770.75   $770.80