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 $218.73   8.668%   $237.6895   $237.69   $237.70   $237.70  
  Purchase #2 $56.60   10.364%   $62.466   $62.47   $62.45   $62.50  
  Purchase #3 $60.50   7.559%   $65.0732   $65.07   $65.05   $65.10  
  Purchase #4 $161.87   8.124%   $175.0203   $175.02   $175.00   $175.00  
  Purchase #5 $234.50   7.524%   $252.1438   $252.14   $252.15   $252.10  
  Purchase #6 $113.89   4.525%   $119.0435   $119.04   $119.05   $119.00  
  Purchase #7 $105.56   13.390%   $119.6945   $119.69   $119.70   $119.70  
  7 purchase totals = $951.65       $1,031.1308   $1,031.12   $1,031.10   $1,031.10