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 $32.79   3.592%   $33.9678   $33.97   $33.95   $34.00  
  Purchase #2 $240.81   8.673%   $261.6955   $261.70   $261.70   $261.70  
  Purchase #3 $225.80   4.138%   $235.1436   $235.14   $235.15   $235.10  
  Purchase #4 $98.81   10.416%   $109.102   $109.10   $109.10   $109.10  
  Purchase #5 $239.58   13.229%   $271.274   $271.27   $271.25   $271.30  
  Purchase #6 $146.53   13.401%   $166.1665   $166.17   $166.15   $166.20  
  Purchase #7 $48.83   10.862%   $54.1339   $54.13   $54.15   $54.10  
  7 purchase totals = $1,033.15       $1,131.4833   $1,131.48   $1,131.45   $1,131.50