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 $249.95   10.190%   $275.4199   $275.42   $275.40   $275.40  
  Purchase #2 $135.42   5.484%   $142.8464   $142.85   $142.85   $142.80  
  Purchase #3 $81.39   3.753%   $84.4446   $84.44   $84.45   $84.40  
  Purchase #4 $178.37   4.752%   $186.8461   $186.85   $186.85   $186.80  
  Purchase #5 $222.61   6.656%   $237.4269   $237.43   $237.45   $237.40  
  Purchase #6 $167.41   5.534%   $176.6745   $176.67   $176.65   $176.70  
  Purchase #7 $93.41   8.845%   $101.6721   $101.67   $101.65   $101.70  
  7 purchase totals = $1,128.56       $1,205.3305   $1,205.33   $1,205.30   $1,205.20