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 $14.43   12.260%   $16.1991   $16.20   $16.20   $16.20  
  Purchase #2 $218.38   8.416%   $236.7589   $236.76   $236.75   $236.80  
  Purchase #3 $83.35   12.727%   $93.958   $93.96   $93.95   $94.00  
  Purchase #4 $182.94   10.581%   $202.2969   $202.30   $202.30   $202.30  
  Purchase #5 $125.92   6.449%   $134.0406   $134.04   $134.05   $134.00  
  Purchase #6 $186.44   6.323%   $198.2286   $198.23   $198.25   $198.20  
  Purchase #7 $49.32   4.502%   $51.5404   $51.54   $51.55   $51.50  
  7 purchase totals = $860.78       $933.0225   $933.03   $933.05   $933.00