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 $231.56   7.651%   $249.2767   $249.28   $249.30   $249.30  
  Purchase #2 $91.94   7.411%   $98.7537   $98.75   $98.75   $98.80  
  Purchase #3 $151.46   7.400%   $162.668   $162.67   $162.65   $162.70  
  Purchase #4 $209.47   4.277%   $218.429   $218.43   $218.45   $218.40  
  Purchase #5 $108.44   5.108%   $113.9791   $113.98   $114.00   $114.00  
  Purchase #6 $249.31   12.565%   $280.6358   $280.64   $280.65   $280.60  
  Purchase #7 $231.53   7.326%   $248.4919   $248.49   $248.50   $248.50  
  7 purchase totals = $1,273.71       $1,372.2342   $1,372.24   $1,372.30   $1,372.30