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 $199.44   7.270%   $213.9393   $213.94   $213.95   $213.90  
  Purchase #2 $209.26   10.602%   $231.4457   $231.45   $231.45   $231.40  
  Purchase #3 $216.38   11.801%   $241.915   $241.92   $241.90   $241.90  
  Purchase #4 $60.48   4.826%   $63.3988   $63.40   $63.40   $63.40  
  Purchase #5 $107.48   7.459%   $115.4969   $115.50   $115.50   $115.50  
  Purchase #6 $124.32   8.589%   $134.9978   $135.00   $135.00   $135.00  
  Purchase #7 $228.31   13.603%   $259.367   $259.37   $259.35   $259.40  
  7 purchase totals = $1,145.67       $1,260.5605   $1,260.58   $1,260.55   $1,260.50