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 $240.82   11.702%   $269.0008   $269.00   $269.00   $269.00  
  Purchase #2 $111.99   9.215%   $122.3099   $122.31   $122.30   $122.30  
  Purchase #3 $23.48   8.259%   $25.4192   $25.42   $25.40   $25.40  
  Purchase #4 $247.62   6.553%   $263.8465   $263.85   $263.85   $263.80  
  Purchase #5 $151.45   3.644%   $156.9688   $156.97   $156.95   $157.00  
  Purchase #6 $13.95   7.578%   $15.0071   $15.01   $15.00   $15.00  
  Purchase #7 $177.26   5.272%   $186.6051   $186.61   $186.60   $186.60  
  7 purchase totals = $966.57       $1,039.1574   $1,039.17   $1,039.10   $1,039.10