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 $224.63   9.608%   $246.2125   $246.21   $246.20   $246.20  
  Purchase #2 $46.27   5.744%   $48.9277   $48.93   $48.95   $48.90  
  Purchase #3 $94.43   7.104%   $101.1383   $101.14   $101.15   $101.10  
  Purchase #4 $61.80   7.543%   $66.4616   $66.46   $66.45   $66.50  
  Purchase #5 $189.55   8.593%   $205.838   $205.84   $205.85   $205.80  
  Purchase #6 $30.85   12.214%   $34.618   $34.62   $34.60   $34.60  
  Purchase #7 $219.99   5.404%   $231.8783   $231.88   $231.90   $231.90  
  7 purchase totals = $867.52       $935.0744   $935.08   $935.10   $935.00