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 $248.79   5.123%   $261.5355   $261.54   $261.55   $261.50  
  Purchase #2 $53.80   5.234%   $56.6159   $56.62   $56.60   $56.60  
  Purchase #3 $145.96   9.853%   $160.3414   $160.34   $160.35   $160.30  
  Purchase #4 $220.94   13.529%   $250.831   $250.83   $250.85   $250.80  
  Purchase #5 $180.93   13.259%   $204.9195   $204.92   $204.90   $204.90  
  Purchase #6 $241.61   7.591%   $259.9506   $259.95   $259.95   $260.00  
  Purchase #7 $175.27   7.502%   $188.4188   $188.42   $188.40   $188.40  
  7 purchase totals = $1,267.30       $1,382.6127   $1,382.62   $1,382.60   $1,382.50