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 $96.28   8.622%   $104.5813   $104.58   $104.60   $104.60  
  Purchase #2 $241.32   11.189%   $268.3213   $268.32   $268.30   $268.30  
  Purchase #3 $35.25   10.273%   $38.8712   $38.87   $38.85   $38.90  
  Purchase #4 $204.55   11.317%   $227.6989   $227.70   $227.70   $227.70  
  Purchase #5 $109.34   5.652%   $115.5199   $115.52   $115.50   $115.50  
  Purchase #6 $157.71   3.783%   $163.6762   $163.68   $163.70   $163.70  
  Purchase #7 $99.75   6.508%   $106.2417   $106.24   $106.25   $106.20  
  7 purchase totals = $944.20       $1,024.9105   $1,024.91   $1,024.90   $1,024.90