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 $116.91   5.615%   $123.4745   $123.47   $123.45   $123.50  
  Purchase #2 $98.81   12.424%   $111.0862   $111.09   $111.10   $111.10  
  Purchase #3 $23.87   9.775%   $26.2033   $26.20   $26.20   $26.20  
  Purchase #4 $78.87   5.792%   $83.4382   $83.44   $83.45   $83.40  
  Purchase #5 $19.52   5.730%   $20.6385   $20.64   $20.65   $20.60  
  Purchase #6 $192.45   11.459%   $214.5028   $214.50   $214.50   $214.50  
  Purchase #7 $238.89   3.542%   $247.3515   $247.35   $247.35   $247.40  
  7 purchase totals = $769.32       $826.6950   $826.69   $826.70   $826.70