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 $159.93   10.230%   $176.2908   $176.29   $176.30   $176.30  
  Purchase #2 $126.51   6.180%   $134.3283   $134.33   $134.35   $134.30  
  Purchase #3 $119.43   12.579%   $134.4531   $134.45   $134.45   $134.50  
  Purchase #4 $181.73   6.637%   $193.7914   $193.79   $193.80   $193.80  
  Purchase #5 $128.38   8.374%   $139.1305   $139.13   $139.15   $139.10  
  Purchase #6 $96.82   8.662%   $105.2065   $105.21   $105.20   $105.20  
  Purchase #7 $168.45   4.474%   $175.9865   $175.99   $176.00   $176.00  
  7 purchase totals = $981.25       $1,059.1871   $1,059.19   $1,059.25   $1,059.20