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 $32.73   5.279%   $34.4578   $34.46   $34.45   $34.50  
  Purchase #2 $141.75   11.411%   $157.9251   $157.93   $157.95   $157.90  
  Purchase #3 $206.46   6.276%   $219.4174   $219.42   $219.40   $219.40  
  Purchase #4 $33.89   4.807%   $35.5191   $35.52   $35.50   $35.50  
  Purchase #5 $235.90   10.769%   $261.3041   $261.30   $261.30   $261.30  
  Purchase #6 $122.91   11.131%   $136.5911   $136.59   $136.60   $136.60  
  Purchase #7 $82.70   5.216%   $87.0136   $87.01   $87.00   $87.00  
  7 purchase totals = $856.34       $932.2282   $932.23   $932.20   $932.20