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 $209.89   10.658%   $232.2601   $232.26   $232.25   $232.30  
  Purchase #2 $248.31   4.508%   $259.5038   $259.50   $259.50   $259.50  
  Purchase #3 $99.68   4.612%   $104.2772   $104.28   $104.30   $104.30  
  Purchase #4 $130.88   12.689%   $147.4874   $147.49   $147.50   $147.50  
  Purchase #5 $139.78   10.873%   $154.9783   $154.98   $155.00   $155.00  
  Purchase #6 $116.99   4.762%   $122.5611   $122.56   $122.55   $122.60  
  Purchase #7 $40.58   12.733%   $45.7471   $45.75   $45.75   $45.70  
  7 purchase totals = $986.11       $1,066.8150   $1,066.82   $1,066.85   $1,066.90