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 $26.34   11.267%   $29.3077   $29.31   $29.30   $29.30  
  Purchase #2 $116.40   9.873%   $127.8922   $127.89   $127.90   $127.90  
  Purchase #3 $152.99   12.232%   $171.7037   $171.70   $171.70   $171.70  
  Purchase #4 $215.67   5.246%   $226.984   $226.98   $227.00   $227.00  
  Purchase #5 $182.64   8.778%   $198.6721   $198.67   $198.65   $198.70  
  Purchase #6 $161.49   10.400%   $178.285   $178.29   $178.30   $178.30  
  Purchase #7 $102.35   12.708%   $115.3566   $115.36   $115.35   $115.40  
  7 purchase totals = $957.88       $1,048.2013   $1,048.20   $1,048.20   $1,048.30