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 $169.62   10.204%   $186.928   $186.93   $186.95   $186.90  
  Purchase #2 $54.99   8.134%   $59.4629   $59.46   $59.45   $59.50  
  Purchase #3 $46.37   13.352%   $52.5613   $52.56   $52.55   $52.60  
  Purchase #4 $237.63   7.306%   $254.9912   $254.99   $255.00   $255.00  
  Purchase #5 $73.83   8.292%   $79.952   $79.95   $79.95   $80.00  
  Purchase #6 $67.54   13.573%   $76.7072   $76.71   $76.70   $76.70  
  Purchase #7 $6.45   9.168%   $7.0413   $7.04   $7.05   $7.00  
  7 purchase totals = $656.43       $717.6439   $717.64   $717.65   $717.70