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 $65.73   13.494%   $74.5996   $74.60   $74.60   $74.60  
  Purchase #2 $128.50   11.822%   $143.6913   $143.69   $143.70   $143.70  
  Purchase #3 $235.77   5.867%   $249.6026   $249.60   $249.60   $249.60  
  Purchase #4 $86.99   11.814%   $97.267   $97.27   $97.25   $97.30  
  Purchase #5 $57.70   7.516%   $62.0367   $62.04   $62.05   $62.00  
  Purchase #6 $164.36   13.727%   $186.9217   $186.92   $186.90   $186.90  
  Purchase #7 $112.62   5.228%   $118.5078   $118.51   $118.50   $118.50  
  7 purchase totals = $851.67       $932.6267   $932.63   $932.60   $932.60