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 $231.42   13.580%   $262.8468   $262.85   $262.85   $262.80  
  Purchase #2 $163.37   5.799%   $172.8438   $172.84   $172.85   $172.80  
  Purchase #3 $113.35   12.274%   $127.2626   $127.26   $127.25   $127.30  
  Purchase #4 $207.38   9.757%   $227.6141   $227.61   $227.60   $227.60  
  Purchase #5 $240.97   11.389%   $268.4141   $268.41   $268.40   $268.40  
  Purchase #6 $211.81   10.484%   $234.0162   $234.02   $234.00   $234.00  
  Purchase #7 $68.41   7.562%   $73.5832   $73.58   $73.60   $73.60  
  7 purchase totals = $1,236.71       $1,366.5808   $1,366.57   $1,366.55   $1,366.50