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 $72.28   8.735%   $78.5937   $78.59   $78.60   $78.60  
  Purchase #2 $235.99   9.200%   $257.7011   $257.70   $257.70   $257.70  
  Purchase #3 $244.73   12.773%   $275.9894   $275.99   $276.00   $276.00  
  Purchase #4 $76.67   5.492%   $80.8807   $80.88   $80.90   $80.90  
  Purchase #5 $76.53   6.490%   $81.4968   $81.50   $81.50   $81.50  
  Purchase #6 $213.93   5.143%   $224.9324   $224.93   $224.95   $224.90  
  Purchase #7 $47.58   11.506%   $53.0546   $53.05   $53.05   $53.10  
  7 purchase totals = $967.71       $1,052.6487   $1,052.64   $1,052.70   $1,052.70