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 $210.43   11.707%   $235.065   $235.07   $235.05   $235.10  
  Purchase #2 $21.59   3.864%   $22.4242   $22.42   $22.40   $22.40  
  Purchase #3 $134.66   3.768%   $139.734   $139.73   $139.75   $139.70  
  Purchase #4 $96.50   7.803%   $104.0299   $104.03   $104.05   $104.00  
  Purchase #5 $234.94   5.871%   $248.7333   $248.73   $248.75   $248.70  
  Purchase #6 $218.97   12.662%   $246.696   $246.70   $246.70   $246.70  
  Purchase #7 $31.62   7.783%   $34.081   $34.08   $34.10   $34.10  
  7 purchase totals = $948.71       $1,030.7634   $1,030.76   $1,030.80   $1,030.70