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 $23.39   12.459%   $26.3042   $26.30   $26.30   $26.30  
  Purchase #2 $222.31   10.646%   $245.9771   $245.98   $246.00   $246.00  
  Purchase #3 $163.78   11.316%   $182.3133   $182.31   $182.30   $182.30  
  Purchase #4 $157.36   11.141%   $174.8915   $174.89   $174.90   $174.90  
  Purchase #5 $242.53   10.331%   $267.5858   $267.59   $267.60   $267.60  
  Purchase #6 $116.55   8.264%   $126.1817   $126.18   $126.20   $126.20  
  Purchase #7 $228.60   13.860%   $260.284   $260.28   $260.30   $260.30  
  7 purchase totals = $1,154.52       $1,283.5376   $1,283.53   $1,283.60   $1,283.60