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 $176.86   13.807%   $201.2791   $201.28   $201.30   $201.30  
  Purchase #2 $59.79   10.469%   $66.0494   $66.05   $66.05   $66.00  
  Purchase #3 $180.82   4.483%   $188.9262   $188.93   $188.95   $188.90  
  Purchase #4 $175.61   7.298%   $188.426   $188.43   $188.45   $188.40  
  Purchase #5 $52.50   6.773%   $56.0558   $56.06   $56.05   $56.10  
  Purchase #6 $39.34   9.685%   $43.1501   $43.15   $43.15   $43.20  
  Purchase #7 $26.50   13.441%   $30.0619   $30.06   $30.05   $30.10  
  7 purchase totals = $711.42       $773.9485   $773.96   $774.00   $774.00