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 $63.33   11.487%   $70.6047   $70.60   $70.60   $70.60  
  Purchase #2 $250.77   4.335%   $261.6409   $261.64   $261.65   $261.60  
  Purchase #3 $56.86   8.267%   $61.5606   $61.56   $61.55   $61.60  
  Purchase #4 $164.75   7.718%   $177.4654   $177.47   $177.45   $177.50  
  Purchase #5 $160.41   8.468%   $173.9935   $173.99   $174.00   $174.00  
  Purchase #6 $150.29   9.502%   $164.5706   $164.57   $164.55   $164.60  
  Purchase #7 $42.53   12.499%   $47.8458   $47.85   $47.85   $47.80  
  7 purchase totals = $888.94       $957.6815   $957.68   $957.65   $957.70