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 $60.90   4.557%   $63.6752   $63.68   $63.70   $63.70  
  Purchase #2 $241.48   4.465%   $252.2621   $252.26   $252.25   $252.30  
  Purchase #3 $177.71   8.154%   $192.2005   $192.20   $192.20   $192.20  
  Purchase #4 $16.94   11.281%   $18.851   $18.85   $18.85   $18.90  
  Purchase #5 $229.50   6.443%   $244.2867   $244.29   $244.30   $244.30  
  Purchase #6 $40.95   5.470%   $43.19   $43.19   $43.20   $43.20  
  Purchase #7 $13.32   6.175%   $14.1425   $14.14   $14.15   $14.10  
  7 purchase totals = $780.80       $828.6080   $828.61   $828.65   $828.70