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 $188.49   8.740%   $204.964   $204.96   $204.95   $205.00  
  Purchase #2 $22.68   4.451%   $23.6895   $23.69   $23.70   $23.70  
  Purchase #3 $104.81   9.535%   $114.8036   $114.80   $114.80   $114.80  
  Purchase #4 $138.55   13.645%   $157.4551   $157.46   $157.45   $157.50  
  Purchase #5 $219.80   11.808%   $245.754   $245.75   $245.75   $245.80  
  Purchase #6 $148.30   6.693%   $158.2257   $158.23   $158.25   $158.20  
  Purchase #7 $46.43   7.277%   $49.8087   $49.81   $49.80   $49.80  
  7 purchase totals = $869.06       $954.7006   $954.70   $954.70   $954.80