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 $88.39   10.595%   $97.7549   $97.75   $97.75   $97.80  
  Purchase #2 $64.82   6.342%   $68.9309   $68.93   $68.95   $68.90  
  Purchase #3 $69.91   8.702%   $75.9936   $75.99   $76.00   $76.00  
  Purchase #4 $23.69   12.595%   $26.6738   $26.67   $26.65   $26.70  
  Purchase #5 $239.58   3.866%   $248.8422   $248.84   $248.85   $248.80  
  Purchase #6 $234.82   3.787%   $243.7126   $243.71   $243.70   $243.70  
  Purchase #7 $30.92   3.511%   $32.0056   $32.01   $32.00   $32.00  
  7 purchase totals = $752.13       $793.9136   $793.90   $793.90   $793.90