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 $23.53   11.322%   $26.1941   $26.19   $26.20   $26.20  
  Purchase #2 $80.54   8.650%   $87.5067   $87.51   $87.50   $87.50  
  Purchase #3 $160.31   13.868%   $182.5418   $182.54   $182.55   $182.50  
  Purchase #4 $139.65   10.690%   $154.5786   $154.58   $154.60   $154.60  
  Purchase #5 $202.93   7.119%   $217.3766   $217.38   $217.40   $217.40  
  Purchase #6 $190.73   4.245%   $198.8265   $198.83   $198.85   $198.80  
  Purchase #7 $219.26   9.614%   $240.3397   $240.34   $240.35   $240.30  
  7 purchase totals = $1,016.95       $1,107.3640   $1,107.37   $1,107.45   $1,107.30