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 $119.38   11.790%   $133.4549   $133.45   $133.45   $133.50  
  Purchase #2 $43.57   10.361%   $48.0843   $48.08   $48.10   $48.10  
  Purchase #3 $118.28   10.673%   $130.904   $130.90   $130.90   $130.90  
  Purchase #4 $85.48   11.845%   $95.6051   $95.61   $95.60   $95.60  
  Purchase #5 $230.42   13.586%   $261.7249   $261.72   $261.70   $261.70  
  Purchase #6 $44.73   11.348%   $49.806   $49.81   $49.80   $49.80  
  Purchase #7 $164.80   11.384%   $183.5608   $183.56   $183.55   $183.60  
  7 purchase totals = $806.66       $903.1400   $903.13   $903.10   $903.20