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 $24.84   6.788%   $26.5261   $26.53   $26.55   $26.50  
  Purchase #2 $152.93   12.216%   $171.6119   $171.61   $171.60   $171.60  
  Purchase #3 $105.30   7.718%   $113.4271   $113.43   $113.45   $113.40  
  Purchase #4 $16.88   7.845%   $18.2042   $18.20   $18.20   $18.20  
  Purchase #5 $166.74   12.707%   $187.9277   $187.93   $187.95   $187.90  
  Purchase #6 $154.32   11.396%   $171.9063   $171.91   $171.90   $171.90  
  Purchase #7 $6.72   3.674%   $6.9669   $6.97   $6.95   $7.00  
  7 purchase totals = $627.73       $696.5702   $696.58   $696.60   $696.50