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 $54.44   11.129%   $60.4986   $60.50   $60.50   $60.50  
  Purchase #2 $234.86   7.483%   $252.4346   $252.43   $252.45   $252.40  
  Purchase #3 $43.57   13.677%   $49.5291   $49.53   $49.55   $49.50  
  Purchase #4 $194.71   11.744%   $217.5767   $217.58   $217.60   $217.60  
  Purchase #5 $249.32   6.306%   $265.0421   $265.04   $265.05   $265.00  
  Purchase #6 $51.30   12.435%   $57.6792   $57.68   $57.70   $57.70  
  Purchase #7 $151.80   9.547%   $166.2923   $166.29   $166.30   $166.30  
  7 purchase totals = $980.00       $1,069.0526   $1,069.05   $1,069.15   $1,069.00