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 $87.63   12.449%   $98.5391   $98.54   $98.55   $98.50  
  Purchase #2 $207.79   8.424%   $225.2942   $225.29   $225.30   $225.30  
  Purchase #3 $203.67   11.144%   $226.367   $226.37   $226.35   $226.40  
  Purchase #4 $78.30   4.460%   $81.7922   $81.79   $81.80   $81.80  
  Purchase #5 $101.36   10.310%   $111.8102   $111.81   $111.80   $111.80  
  Purchase #6 $164.57   10.265%   $181.4631   $181.46   $181.45   $181.50  
  Purchase #7 $157.99   10.581%   $174.7069   $174.71   $174.70   $174.70  
  7 purchase totals = $1,001.31       $1,099.9727   $1,099.97   $1,099.95   $1,100.00