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 $54.37   8.211%   $58.8343   $58.83   $58.85   $58.80  
  Purchase #2 $57.83   12.836%   $65.2531   $65.25   $65.25   $65.30  
  Purchase #3 $91.48   13.801%   $104.1052   $104.11   $104.10   $104.10  
  Purchase #4 $133.31   4.500%   $139.309   $139.31   $139.30   $139.30  
  Purchase #5 $186.84   8.291%   $202.3309   $202.33   $202.35   $202.30  
  Purchase #6 $167.25   10.338%   $184.5403   $184.54   $184.55   $184.50  
  Purchase #7 $177.41   13.552%   $201.4526   $201.45   $201.45   $201.50  
  7 purchase totals = $868.49       $955.8254   $955.82   $955.85   $955.80