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 $67.31   13.587%   $76.4554   $76.46   $76.45   $76.50  
  Purchase #2 $128.28   10.292%   $141.4826   $141.48   $141.50   $141.50  
  Purchase #3 $202.94   11.865%   $227.0188   $227.02   $227.00   $227.00  
  Purchase #4 $206.80   6.595%   $220.4385   $220.44   $220.45   $220.40  
  Purchase #5 $202.37   7.229%   $216.9993   $217.00   $217.00   $217.00  
  Purchase #6 $45.94   4.328%   $47.9283   $47.93   $47.95   $47.90  
  Purchase #7 $26.42   9.792%   $29.007   $29.01   $29.00   $29.00  
  7 purchase totals = $880.06       $959.3299   $959.34   $959.35   $959.30