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 $224.38   5.516%   $236.7568   $236.76   $236.75   $236.80  
  Purchase #2 $163.73   9.541%   $179.3515   $179.35   $179.35   $179.40  
  Purchase #3 $201.49   13.564%   $228.8201   $228.82   $228.80   $228.80  
  Purchase #4 $27.86   9.511%   $30.5098   $30.51   $30.50   $30.50  
  Purchase #5 $62.89   7.576%   $67.6545   $67.65   $67.65   $67.70  
  Purchase #6 $203.85   12.873%   $230.0916   $230.09   $230.10   $230.10  
  Purchase #7 $67.83   12.276%   $76.1568   $76.16   $76.15   $76.20  
  7 purchase totals = $952.03       $1,049.3411   $1,049.34   $1,049.30   $1,049.50