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 $91.89   4.617%   $96.1326   $96.13   $96.15   $96.10  
  Purchase #2 $83.71   10.272%   $92.3087   $92.31   $92.30   $92.30  
  Purchase #3 $123.91   8.335%   $134.2379   $134.24   $134.25   $134.20  
  Purchase #4 $73.73   12.814%   $83.1778   $83.18   $83.20   $83.20  
  Purchase #5 $193.87   4.494%   $202.5825   $202.58   $202.60   $202.60  
  Purchase #6 $66.88   3.796%   $69.4188   $69.42   $69.40   $69.40  
  Purchase #7 $196.41   11.114%   $218.239   $218.24   $218.25   $218.20  
  7 purchase totals = $830.40       $896.0973   $896.10   $896.15   $896.00