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 $55.95   12.814%   $63.1194   $63.12   $63.10   $63.10  
  Purchase #2 $24.60   13.432%   $27.9043   $27.90   $27.90   $27.90  
  Purchase #3 $198.63   7.858%   $214.2383   $214.24   $214.25   $214.20  
  Purchase #4 $158.48   11.396%   $176.5404   $176.54   $176.55   $176.50  
  Purchase #5 $35.60   12.766%   $40.1447   $40.14   $40.15   $40.10  
  Purchase #6 $180.50   4.770%   $189.1099   $189.11   $189.10   $189.10  
  Purchase #7 $59.81   3.651%   $61.9937   $61.99   $62.00   $62.00  
  7 purchase totals = $713.57       $773.0507   $773.04   $773.05   $772.90