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 $124.46   9.723%   $136.5612   $136.56   $136.55   $136.60  
  Purchase #2 $177.39   8.367%   $192.2322   $192.23   $192.25   $192.20  
  Purchase #3 $136.77   8.726%   $148.7046   $148.70   $148.70   $148.70  
  Purchase #4 $128.42   5.702%   $135.7425   $135.74   $135.75   $135.70  
  Purchase #5 $239.80   12.156%   $268.9501   $268.95   $268.95   $269.00  
  Purchase #6 $10.92   11.836%   $12.2125   $12.21   $12.20   $12.20  
  Purchase #7 $223.90   3.542%   $231.8305   $231.83   $231.85   $231.80  
  7 purchase totals = $1,041.66       $1,126.2336   $1,126.22   $1,126.25   $1,126.20