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 $61.81   12.372%   $69.4571   $69.46   $69.45   $69.50  
  Purchase #2 $246.64   5.457%   $260.0991   $260.10   $260.10   $260.10  
  Purchase #3 $205.67   9.407%   $225.0174   $225.02   $225.00   $225.00  
  Purchase #4 $238.61   13.156%   $270.0015   $270.00   $270.00   $270.00  
  Purchase #5 $78.88   12.763%   $88.9475   $88.95   $88.95   $88.90  
  Purchase #6 $40.95   5.216%   $43.086   $43.09   $43.10   $43.10  
  Purchase #7 $66.48   7.466%   $71.4434   $71.44   $71.45   $71.40  
  7 purchase totals = $939.04       $1,028.0520   $1,028.06   $1,028.05   $1,028.00