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 $82.62   13.144%   $93.4796   $93.48   $93.50   $93.50  
  Purchase #2 $231.58   3.302%   $239.2268   $239.23   $239.25   $239.20  
  Purchase #3 $197.56   7.855%   $213.0783   $213.08   $213.10   $213.10  
  Purchase #4 $124.91   9.720%   $137.0513   $137.05   $137.05   $137.10  
  Purchase #5 $58.57   10.441%   $64.6853   $64.69   $64.70   $64.70  
  Purchase #6 $162.71   5.162%   $171.1091   $171.11   $171.10   $171.10  
  Purchase #7 $81.86   11.154%   $90.9907   $90.99   $91.00   $91.00  
  7 purchase totals = $939.81       $1,009.6211   $1,009.63   $1,009.70   $1,009.70