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 $119.27   12.522%   $134.205   $134.21   $134.20   $134.20  
  Purchase #2 $178.56   6.477%   $190.1253   $190.13   $190.15   $190.10  
  Purchase #3 $68.26   11.424%   $76.058   $76.06   $76.05   $76.10  
  Purchase #4 $108.54   8.773%   $118.0622   $118.06   $118.05   $118.10  
  Purchase #5 $92.45   4.354%   $96.4753   $96.48   $96.50   $96.50  
  Purchase #6 $38.72   6.591%   $41.272   $41.27   $41.25   $41.30  
  Purchase #7 $158.84   11.501%   $177.1082   $177.11   $177.10   $177.10  
  7 purchase totals = $764.64       $833.3060   $833.32   $833.30   $833.40