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 $241.63   8.390%   $261.9028   $261.90   $261.90   $261.90  
  Purchase #2 $71.62   8.532%   $77.7306   $77.73   $77.75   $77.70  
  Purchase #3 $87.39   3.539%   $90.4827   $90.48   $90.50   $90.50  
  Purchase #4 $85.89   13.599%   $97.5702   $97.57   $97.55   $97.60  
  Purchase #5 $123.39   9.335%   $134.9085   $134.91   $134.90   $134.90  
  Purchase #6 $74.79   13.265%   $84.7109   $84.71   $84.70   $84.70  
  Purchase #7 $45.84   4.238%   $47.7827   $47.78   $47.80   $47.80  
  7 purchase totals = $730.55       $795.0884   $795.08   $795.10   $795.10