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 $248.91   6.860%   $265.9852   $265.99   $266.00   $266.00  
  Purchase #2 $232.28   3.767%   $241.03   $241.03   $241.05   $241.00  
  Purchase #3 $142.84   4.536%   $149.3192   $149.32   $149.30   $149.30  
  Purchase #4 $32.89   8.314%   $35.6245   $35.62   $35.60   $35.60  
  Purchase #5 $31.57   9.824%   $34.6714   $34.67   $34.65   $34.70  
  Purchase #6 $239.86   11.843%   $268.2666   $268.27   $268.25   $268.30  
  Purchase #7 $150.86   6.710%   $160.9827   $160.98   $161.00   $161.00  
  7 purchase totals = $1,079.21       $1,155.8796   $1,155.88   $1,155.85   $1,155.90