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 $238.87   10.610%   $264.2141   $264.21   $264.20   $264.20  
  Purchase #2 $224.78   10.555%   $248.5055   $248.51   $248.50   $248.50  
  Purchase #3 $36.55   8.696%   $39.7284   $39.73   $39.75   $39.70  
  Purchase #4 $103.61   11.275%   $115.292   $115.29   $115.30   $115.30  
  Purchase #5 $62.26   11.392%   $69.3527   $69.35   $69.35   $69.40  
  Purchase #6 $219.61   4.605%   $229.723   $229.72   $229.70   $229.70  
  Purchase #7 $78.40   11.711%   $87.5814   $87.58   $87.60   $87.60  
  7 purchase totals = $964.08       $1,054.3971   $1,054.39   $1,054.40   $1,054.40