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 $88.86   4.362%   $92.7361   $92.74   $92.75   $92.70  
  Purchase #2 $76.27   3.184%   $78.6984   $78.70   $78.70   $78.70  
  Purchase #3 $156.76   6.291%   $166.6218   $166.62   $166.60   $166.60  
  Purchase #4 $213.96   8.799%   $232.7863   $232.79   $232.80   $232.80  
  Purchase #5 $106.90   11.701%   $119.4084   $119.41   $119.40   $119.40  
  Purchase #6 $54.48   7.719%   $58.6853   $58.69   $58.70   $58.70  
  Purchase #7 $104.31   13.230%   $118.1102   $118.11   $118.10   $118.10  
  7 purchase totals = $801.54       $867.0465   $867.06   $867.05   $867.00