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 $88.60   6.627%   $94.4715   $94.47   $94.45   $94.50  
  Purchase #2 $73.58   6.504%   $78.3656   $78.37   $78.35   $78.40  
  Purchase #3 $94.89   10.656%   $105.0015   $105.00   $105.00   $105.00  
  Purchase #4 $216.98   9.432%   $237.4456   $237.45   $237.45   $237.40  
  Purchase #5 $193.65   5.184%   $203.6888   $203.69   $203.70   $203.70  
  Purchase #6 $61.70   4.382%   $64.4037   $64.40   $64.40   $64.40  
  Purchase #7 $71.45   7.451%   $76.7737   $76.77   $76.75   $76.80  
  7 purchase totals = $800.85       $860.1504   $860.15   $860.10   $860.20