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 $11.68   5.845%   $12.3627   $12.36   $12.35   $12.40  
  Purchase #2 $182.90   13.362%   $207.3391   $207.34   $207.35   $207.30  
  Purchase #3 $242.36   4.233%   $252.6191   $252.62   $252.60   $252.60  
  Purchase #4 $196.97   4.819%   $206.462   $206.46   $206.45   $206.50  
  Purchase #5 $154.61   7.155%   $165.6723   $165.67   $165.65   $165.70  
  Purchase #6 $168.74   8.266%   $182.688   $182.69   $182.70   $182.70  
  Purchase #7 $212.80   5.425%   $224.3444   $224.34   $224.35   $224.30  
  7 purchase totals = $1,170.06       $1,251.4876   $1,251.48   $1,251.45   $1,251.50