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 $59.27   8.406%   $64.2522   $64.25   $64.25   $64.30  
  Purchase #2 $181.89   12.546%   $204.7099   $204.71   $204.70   $204.70  
  Purchase #3 $177.25   11.393%   $197.4441   $197.44   $197.45   $197.40  
  Purchase #4 $112.88   7.318%   $121.1406   $121.14   $121.15   $121.10  
  Purchase #5 $227.36   3.497%   $235.3108   $235.31   $235.30   $235.30  
  Purchase #6 $152.87   6.534%   $162.8585   $162.86   $162.85   $162.90  
  Purchase #7 $57.88   10.482%   $63.947   $63.95   $63.95   $63.90  
  7 purchase totals = $969.40       $1,049.6631   $1,049.66   $1,049.65   $1,049.60