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 $241.68   5.583%   $255.173   $255.17   $255.15   $255.20  
  Purchase #2 $19.69   12.513%   $22.1538   $22.15   $22.15   $22.20  
  Purchase #3 $163.42   9.809%   $179.4499   $179.45   $179.45   $179.40  
  Purchase #4 $64.44   3.873%   $66.9358   $66.94   $66.95   $66.90  
  Purchase #5 $114.70   8.372%   $124.3027   $124.30   $124.30   $124.30  
  Purchase #6 $57.30   3.783%   $59.4677   $59.47   $59.45   $59.50  
  Purchase #7 $224.51   7.499%   $241.346   $241.35   $241.35   $241.30  
  7 purchase totals = $885.74       $948.8289   $948.83   $948.80   $948.80