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 $140.81   11.146%   $156.5047   $156.50   $156.50   $156.50  
  Purchase #2 $247.86   8.741%   $269.5254   $269.53   $269.55   $269.50  
  Purchase #3 $22.93   10.432%   $25.3221   $25.32   $25.30   $25.30  
  Purchase #4 $172.67   11.596%   $192.6928   $192.69   $192.70   $192.70  
  Purchase #5 $232.44   11.600%   $259.403   $259.40   $259.40   $259.40  
  Purchase #6 $176.95   8.767%   $192.4632   $192.46   $192.45   $192.50  
  Purchase #7 $58.61   3.346%   $60.5711   $60.57   $60.55   $60.60  
  7 purchase totals = $1,052.27       $1,156.4823   $1,156.47   $1,156.45   $1,156.50