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 $129.85   8.764%   $141.2301   $141.23   $141.25   $141.20  
  Purchase #2 $13.56   10.191%   $14.9419   $14.94   $14.95   $14.90  
  Purchase #3 $230.66   4.463%   $240.9544   $240.95   $240.95   $241.00  
  Purchase #4 $250.69   5.349%   $264.0994   $264.10   $264.10   $264.10  
  Purchase #5 $35.75   5.104%   $37.5747   $37.57   $37.55   $37.60  
  Purchase #6 $27.25   10.276%   $30.0502   $30.05   $30.05   $30.10  
  Purchase #7 $207.26   9.830%   $227.6337   $227.63   $227.65   $227.60  
  7 purchase totals = $895.02       $956.4844   $956.47   $956.50   $956.50