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 $106.57   12.289%   $119.6664   $119.67   $119.65   $119.70  
  Purchase #2 $105.85   10.814%   $117.2966   $117.30   $117.30   $117.30  
  Purchase #3 $9.35   12.830%   $10.5496   $10.55   $10.55   $10.50  
  Purchase #4 $96.93   10.587%   $107.192   $107.19   $107.20   $107.20  
  Purchase #5 $140.88   4.808%   $147.6535   $147.65   $147.65   $147.70  
  Purchase #6 $53.97   6.551%   $57.5056   $57.51   $57.50   $57.50  
  Purchase #7 $109.65   4.215%   $114.2717   $114.27   $114.25   $114.30  
  7 purchase totals = $623.20       $674.1354   $674.14   $674.10   $674.20