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 $94.62   10.610%   $104.6592   $104.66   $104.65   $104.70  
  Purchase #2 $228.93   11.170%   $254.5015   $254.50   $254.50   $254.50  
  Purchase #3 $198.75   13.689%   $225.9569   $225.96   $225.95   $226.00  
  Purchase #4 $233.25   10.391%   $257.487   $257.49   $257.50   $257.50  
  Purchase #5 $176.71   3.541%   $182.9673   $182.97   $182.95   $183.00  
  Purchase #6 $238.50   9.819%   $261.9183   $261.92   $261.90   $261.90  
  Purchase #7 $205.83   4.235%   $214.5469   $214.55   $214.55   $214.50  
  7 purchase totals = $1,376.59       $1,502.0371   $1,502.05   $1,502.00   $1,502.10