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 $227.40   6.449%   $242.065   $242.07   $242.05   $242.10  
  Purchase #2 $41.75   12.323%   $46.8949   $46.89   $46.90   $46.90  
  Purchase #3 $54.41   6.683%   $58.0462   $58.05   $58.05   $58.00  
  Purchase #4 $44.26   6.736%   $47.2414   $47.24   $47.25   $47.20  
  Purchase #5 $240.66   4.620%   $251.7785   $251.78   $251.80   $251.80  
  Purchase #6 $218.70   7.306%   $234.6782   $234.68   $234.70   $234.70  
  Purchase #7 $164.70   8.223%   $178.2433   $178.24   $178.25   $178.20  
  7 purchase totals = $991.88       $1,058.9475   $1,058.95   $1,059.00   $1,058.90