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 $247.44   6.721%   $264.0704   $264.07   $264.05   $264.10  
  Purchase #2 $238.47   4.186%   $248.4524   $248.45   $248.45   $248.50  
  Purchase #3 $174.66   6.519%   $186.0461   $186.05   $186.05   $186.00  
  Purchase #4 $154.34   12.377%   $173.4427   $173.44   $173.45   $173.40  
  Purchase #5 $5.83   4.467%   $6.0904   $6.09   $6.10   $6.10  
  Purchase #6 $14.58   11.783%   $16.298   $16.30   $16.30   $16.30  
  Purchase #7 $38.87   3.707%   $40.3109   $40.31   $40.30   $40.30  
  7 purchase totals = $874.19       $934.7109   $934.71   $934.70   $934.70