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 $22.95   4.368%   $23.9525   $23.95   $23.95   $24.00  
  Purchase #2 $109.81   8.345%   $118.9736   $118.97   $118.95   $119.00  
  Purchase #3 $122.60   8.249%   $132.7133   $132.71   $132.70   $132.70  
  Purchase #4 $58.81   8.355%   $63.7236   $63.72   $63.70   $63.70  
  Purchase #5 $119.92   13.292%   $135.8598   $135.86   $135.85   $135.90  
  Purchase #6 $22.68   4.805%   $23.7698   $23.77   $23.75   $23.80  
  Purchase #7 $66.31   3.126%   $68.3829   $68.38   $68.40   $68.40  
  7 purchase totals = $523.08       $567.3755   $567.36   $567.30   $567.50