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 $213.69   10.304%   $235.7086   $235.71   $235.70   $235.70  
  Purchase #2 $35.86   12.257%   $40.2554   $40.26   $40.25   $40.30  
  Purchase #3 $199.42   9.401%   $218.1675   $218.17   $218.15   $218.20  
  Purchase #4 $241.32   4.562%   $252.329   $252.33   $252.35   $252.30  
  Purchase #5 $135.79   3.632%   $140.7219   $140.72   $140.70   $140.70  
  Purchase #6 $178.26   7.409%   $191.4673   $191.47   $191.45   $191.50  
  Purchase #7 $158.51   11.417%   $176.6071   $176.61   $176.60   $176.60  
  7 purchase totals = $1,162.85       $1,255.2568   $1,255.27   $1,255.20   $1,255.30