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 $13.86   6.247%   $14.7258   $14.73   $14.75   $14.70  
  Purchase #2 $228.75   7.559%   $246.0412   $246.04   $246.05   $246.00  
  Purchase #3 $155.81   12.816%   $175.7786   $175.78   $175.80   $175.80  
  Purchase #4 $199.77   11.742%   $223.227   $223.23   $223.25   $223.20  
  Purchase #5 $110.77   3.681%   $114.8474   $114.85   $114.85   $114.80  
  Purchase #6 $41.88   10.818%   $46.4106   $46.41   $46.40   $46.40  
  Purchase #7 $38.48   12.508%   $43.2931   $43.29   $43.30   $43.30  
  7 purchase totals = $789.32       $864.3237   $864.33   $864.40   $864.20