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 $166.75   5.458%   $175.8512   $175.85   $175.85   $175.90  
  Purchase #2 $244.70   7.306%   $262.5778   $262.58   $262.60   $262.60  
  Purchase #3 $123.48   12.230%   $138.5816   $138.58   $138.60   $138.60  
  Purchase #4 $208.71   12.445%   $234.684   $234.68   $234.70   $234.70  
  Purchase #5 $163.86   5.451%   $172.792   $172.79   $172.80   $172.80  
  Purchase #6 $227.90   10.850%   $252.6272   $252.63   $252.65   $252.60  
  Purchase #7 $123.99   4.399%   $129.4443   $129.44   $129.45   $129.40  
  7 purchase totals = $1,259.39       $1,366.5581   $1,366.55   $1,366.65   $1,366.60