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 $236.29   5.201%   $248.5794   $248.58   $248.60   $248.60  
  Purchase #2 $250.41   13.304%   $283.7245   $283.72   $283.70   $283.70  
  Purchase #3 $120.63   3.146%   $124.425   $124.43   $124.45   $124.40  
  Purchase #4 $6.84   5.681%   $7.2286   $7.23   $7.25   $7.20  
  Purchase #5 $51.87   8.529%   $56.294   $56.29   $56.30   $56.30  
  Purchase #6 $95.48   12.294%   $107.2183   $107.22   $107.20   $107.20  
  Purchase #7 $5.31   8.524%   $5.7626   $5.76   $5.75   $5.80  
  7 purchase totals = $766.83       $833.2324   $833.23   $833.25   $833.20