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 $248.53   6.621%   $264.9852   $264.99   $265.00   $265.00  
  Purchase #2 $110.48   3.873%   $114.7589   $114.76   $114.75   $114.80  
  Purchase #3 $19.74   4.294%   $20.5876   $20.59   $20.60   $20.60  
  Purchase #4 $200.38   4.396%   $209.1887   $209.19   $209.20   $209.20  
  Purchase #5 $179.86   3.418%   $186.0076   $186.01   $186.00   $186.00  
  Purchase #6 $35.76   6.257%   $37.9975   $38.00   $38.00   $38.00  
  Purchase #7 $83.60   11.802%   $93.4665   $93.47   $93.45   $93.50  
  7 purchase totals = $878.35       $926.9920   $927.01   $927.00   $927.10