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 $182.74   13.336%   $207.1102   $207.11   $207.10   $207.10  
  Purchase #2 $175.75   10.115%   $193.5271   $193.53   $193.55   $193.50  
  Purchase #3 $23.36   11.768%   $26.109   $26.11   $26.10   $26.10  
  Purchase #4 $142.90   8.156%   $154.5549   $154.55   $154.55   $154.60  
  Purchase #5 $31.88   4.519%   $33.3207   $33.32   $33.30   $33.30  
  Purchase #6 $68.27   6.469%   $72.6864   $72.69   $72.70   $72.70  
  Purchase #7 $26.59   10.332%   $29.3373   $29.34   $29.35   $29.30  
  7 purchase totals = $651.49       $716.6456   $716.65   $716.65   $716.60