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 $208.86   7.331%   $224.1715   $224.17   $224.15   $224.20  
  Purchase #2 $110.75   3.335%   $114.4435   $114.44   $114.45   $114.40  
  Purchase #3 $203.39   3.692%   $210.8992   $210.90   $210.90   $210.90  
  Purchase #4 $123.58   9.148%   $134.8851   $134.89   $134.90   $134.90  
  Purchase #5 $150.68   9.489%   $164.978   $164.98   $165.00   $165.00  
  Purchase #6 $164.51   11.264%   $183.0404   $183.04   $183.05   $183.00  
  Purchase #7 $216.85   6.554%   $231.0623   $231.06   $231.05   $231.10  
  7 purchase totals = $1,178.62       $1,263.4800   $1,263.48   $1,263.50   $1,263.50