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 $14.60   13.653%   $16.5933   $16.59   $16.60   $16.60  
  Purchase #2 $198.66   5.835%   $210.2518   $210.25   $210.25   $210.30  
  Purchase #3 $9.26   5.799%   $9.797   $9.80   $9.80   $9.80  
  Purchase #4 $32.55   11.662%   $36.346   $36.35   $36.35   $36.30  
  Purchase #5 $180.41   9.868%   $198.2129   $198.21   $198.20   $198.20  
  Purchase #6 $190.29   12.228%   $213.5587   $213.56   $213.55   $213.60  
  Purchase #7 $175.31   4.192%   $182.659   $182.66   $182.65   $182.70  
  7 purchase totals = $801.08       $867.4187   $867.42   $867.40   $867.50