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 $96.39   10.149%   $106.1726   $106.17   $106.15   $106.20  
  Purchase #2 $212.89   8.696%   $231.4029   $231.40   $231.40   $231.40  
  Purchase #3 $51.90   8.822%   $56.4786   $56.48   $56.50   $56.50  
  Purchase #4 $57.88   12.461%   $65.0924   $65.09   $65.10   $65.10  
  Purchase #5 $57.54   13.790%   $65.4748   $65.47   $65.45   $65.50  
  Purchase #6 $56.28   13.515%   $63.8862   $63.89   $63.90   $63.90  
  Purchase #7 $180.79   11.286%   $201.194   $201.19   $201.20   $201.20  
  7 purchase totals = $713.67       $789.7015   $789.69   $789.70   $789.80