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 $196.97   6.671%   $210.1099   $210.11   $210.10   $210.10  
  Purchase #2 $134.48   13.315%   $152.386   $152.39   $152.40   $152.40  
  Purchase #3 $151.68   8.568%   $164.6759   $164.68   $164.70   $164.70  
  Purchase #4 $114.26   8.186%   $123.6133   $123.61   $123.60   $123.60  
  Purchase #5 $56.28   12.369%   $63.2413   $63.24   $63.25   $63.20  
  Purchase #6 $101.64   8.537%   $110.317   $110.32   $110.30   $110.30  
  Purchase #7 $48.99   7.719%   $52.7715   $52.77   $52.75   $52.80  
  7 purchase totals = $804.30       $877.1149   $877.12   $877.10   $877.10