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 $48.85   8.727%   $53.1131   $53.11   $53.10   $53.10  
  Purchase #2 $198.26   4.134%   $206.4561   $206.46   $206.45   $206.50  
  Purchase #3 $160.58   9.477%   $175.7982   $175.80   $175.80   $175.80  
  Purchase #4 $64.26   12.351%   $72.1968   $72.20   $72.20   $72.20  
  Purchase #5 $145.51   13.118%   $164.598   $164.60   $164.60   $164.60  
  Purchase #6 $247.50   3.161%   $255.3235   $255.32   $255.30   $255.30  
  Purchase #7 $32.70   5.859%   $34.6159   $34.62   $34.60   $34.60  
  7 purchase totals = $897.66       $962.1016   $962.11   $962.05   $962.10