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 $243.29   5.611%   $256.941   $256.94   $256.95   $256.90  
  Purchase #2 $236.49   5.816%   $250.2443   $250.24   $250.25   $250.20  
  Purchase #3 $73.82   4.249%   $76.9566   $76.96   $76.95   $77.00  
  Purchase #4 $67.88   4.119%   $70.676   $70.68   $70.70   $70.70  
  Purchase #5 $196.50   5.850%   $207.9953   $208.00   $208.00   $208.00  
  Purchase #6 $211.54   9.488%   $231.6109   $231.61   $231.60   $231.60  
  Purchase #7 $177.59   13.679%   $201.8825   $201.88   $201.90   $201.90  
  7 purchase totals = $1,207.11       $1,296.3066   $1,296.31   $1,296.35   $1,296.30