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 $231.28   9.524%   $253.3071   $253.31   $253.30   $253.30  
  Purchase #2 $249.34   13.305%   $282.5147   $282.51   $282.50   $282.50  
  Purchase #3 $111.86   6.603%   $119.2461   $119.25   $119.25   $119.20  
  Purchase #4 $233.26   9.645%   $255.7579   $255.76   $255.75   $255.80  
  Purchase #5 $96.65   8.280%   $104.6526   $104.65   $104.65   $104.70  
  Purchase #6 $132.91   3.385%   $137.409   $137.41   $137.40   $137.40  
  Purchase #7 $154.38   4.590%   $161.466   $161.47   $161.45   $161.50  
  7 purchase totals = $1,209.68       $1,314.3534   $1,314.36   $1,314.30   $1,314.40