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 $182.32   13.254%   $206.4847   $206.48   $206.50   $206.50  
  Purchase #2 $147.43   12.136%   $165.3221   $165.32   $165.30   $165.30  
  Purchase #3 $164.41   8.719%   $178.7449   $178.74   $178.75   $178.70  
  Purchase #4 $180.48   3.786%   $187.313   $187.31   $187.30   $187.30  
  Purchase #5 $151.57   4.706%   $158.7029   $158.70   $158.70   $158.70  
  Purchase #6 $59.90   8.182%   $64.801   $64.80   $64.80   $64.80  
  Purchase #7 $67.41   10.699%   $74.6222   $74.62   $74.60   $74.60  
  7 purchase totals = $953.52       $1,035.9908   $1,035.97   $1,035.95   $1,035.90