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 $127.60   4.627%   $133.5041   $133.50   $133.50   $133.50  
  Purchase #2 $37.29   11.133%   $41.4415   $41.44   $41.45   $41.40  
  Purchase #3 $160.92   11.488%   $179.4065   $179.41   $179.40   $179.40  
  Purchase #4 $60.41   5.397%   $63.6703   $63.67   $63.65   $63.70  
  Purchase #5 $236.44   10.613%   $261.5334   $261.53   $261.55   $261.50  
  Purchase #6 $193.48   11.866%   $216.4383   $216.44   $216.45   $216.40  
  Purchase #7 $237.70   10.788%   $263.3431   $263.34   $263.35   $263.30  
  7 purchase totals = $1,053.84       $1,159.3372   $1,159.33   $1,159.35   $1,159.20