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 $70.87   8.540%   $76.9223   $76.92   $76.90   $76.90  
  Purchase #2 $106.75   6.752%   $113.9578   $113.96   $113.95   $114.00  
  Purchase #3 $28.71   6.780%   $30.6565   $30.66   $30.65   $30.70  
  Purchase #4 $98.31   7.774%   $105.9526   $105.95   $105.95   $106.00  
  Purchase #5 $66.75   13.174%   $75.5436   $75.54   $75.55   $75.50  
  Purchase #6 $201.85   10.111%   $222.2591   $222.26   $222.25   $222.30  
  Purchase #7 $69.59   6.199%   $73.9039   $73.90   $73.90   $73.90  
  7 purchase totals = $642.83       $699.1958   $699.19   $699.15   $699.30