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 $66.88   13.696%   $76.0399   $76.04   $76.05   $76.00  
  Purchase #2 $157.48   8.558%   $170.9571   $170.96   $170.95   $171.00  
  Purchase #3 $67.96   11.661%   $75.8848   $75.88   $75.90   $75.90  
  Purchase #4 $214.42   11.385%   $238.8317   $238.83   $238.85   $238.80  
  Purchase #5 $214.71   6.184%   $227.9877   $227.99   $228.00   $228.00  
  Purchase #6 $60.35   7.420%   $64.828   $64.83   $64.85   $64.80  
  Purchase #7 $20.27   6.653%   $21.6186   $21.62   $21.60   $21.60  
  7 purchase totals = $802.07       $876.1478   $876.15   $876.20   $876.10