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 $178.61   4.121%   $185.9705   $185.97   $185.95   $186.00  
  Purchase #2 $26.96   4.856%   $28.2692   $28.27   $28.25   $28.30  
  Purchase #3 $126.62   4.231%   $131.9773   $131.98   $132.00   $132.00  
  Purchase #4 $122.98   3.193%   $126.9068   $126.91   $126.90   $126.90  
  Purchase #5 $84.32   9.848%   $92.6238   $92.62   $92.60   $92.60  
  Purchase #6 $10.25   9.309%   $11.2042   $11.20   $11.20   $11.20  
  Purchase #7 $165.67   5.126%   $174.1622   $174.16   $174.15   $174.20  
  7 purchase totals = $715.41       $751.1140   $751.11   $751.05   $751.20