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 $250.28   6.186%   $265.7623   $265.76   $265.75   $265.80  
  Purchase #2 $211.51   13.617%   $240.3113   $240.31   $240.30   $240.30  
  Purchase #3 $150.88   13.494%   $171.2397   $171.24   $171.25   $171.20  
  Purchase #4 $49.80   11.857%   $55.7048   $55.70   $55.70   $55.70  
  Purchase #5 $206.80   9.755%   $226.9733   $226.97   $226.95   $227.00  
  Purchase #6 $175.58   13.329%   $198.9831   $198.98   $199.00   $199.00  
  Purchase #7 $118.49   12.495%   $133.2953   $133.30   $133.30   $133.30  
  7 purchase totals = $1,163.34       $1,292.2698   $1,292.26   $1,292.25   $1,292.30