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 $60.63   7.755%   $65.3319   $65.33   $65.35   $65.30  
  Purchase #2 $220.37   6.602%   $234.9188   $234.92   $234.90   $234.90  
  Purchase #3 $222.35   10.857%   $246.4905   $246.49   $246.50   $246.50  
  Purchase #4 $26.49   5.167%   $27.8587   $27.86   $27.85   $27.90  
  Purchase #5 $66.69   6.244%   $70.8541   $70.85   $70.85   $70.90  
  Purchase #6 $205.76   9.694%   $225.7064   $225.71   $225.70   $225.70  
  Purchase #7 $208.62   9.498%   $228.4347   $228.43   $228.45   $228.40  
  7 purchase totals = $1,010.91       $1,099.5951   $1,099.59   $1,099.60   $1,099.60