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 $228.48   6.547%   $243.4386   $243.44   $243.45   $243.40  
  Purchase #2 $186.91   5.535%   $197.2555   $197.26   $197.25   $197.30  
  Purchase #3 $110.53   3.225%   $114.0946   $114.09   $114.10   $114.10  
  Purchase #4 $53.41   6.318%   $56.7844   $56.78   $56.80   $56.80  
  Purchase #5 $125.38   12.626%   $141.2105   $141.21   $141.20   $141.20  
  Purchase #6 $170.25   11.231%   $189.3708   $189.37   $189.35   $189.40  
  Purchase #7 $65.28   10.149%   $71.9053   $71.91   $71.90   $71.90  
  7 purchase totals = $940.24       $1,014.0597   $1,014.06   $1,014.05   $1,014.10