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 $124.73   4.375%   $130.1869   $130.19   $130.20   $130.20  
  Purchase #2 $51.79   3.382%   $53.5415   $53.54   $53.55   $53.50  
  Purchase #3 $126.47   3.139%   $130.4399   $130.44   $130.45   $130.40  
  Purchase #4 $161.83   3.544%   $167.5653   $167.57   $167.55   $167.60  
  Purchase #5 $174.79   4.817%   $183.2096   $183.21   $183.20   $183.20  
  Purchase #6 $250.92   4.403%   $261.968   $261.97   $261.95   $262.00  
  Purchase #7 $34.79   12.329%   $39.0793   $39.08   $39.10   $39.10  
  7 purchase totals = $925.32       $965.9905   $966.00   $966.00   $966.00