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   9.492%   $263.6786   $263.68   $263.70   $263.70  
  Purchase #2 $20.42   8.696%   $22.1957   $22.20   $22.20   $22.20  
  Purchase #3 $153.28   7.608%   $164.9415   $164.94   $164.95   $164.90  
  Purchase #4 $219.33   11.821%   $245.257   $245.26   $245.25   $245.30  
  Purchase #5 $52.86   9.635%   $57.9531   $57.95   $57.95   $58.00  
  Purchase #6 $13.67   10.221%   $15.0672   $15.07   $15.05   $15.10  
  Purchase #7 $210.50   11.854%   $235.4527   $235.45   $235.45   $235.50  
  7 purchase totals = $910.88       $1,004.5458   $1,004.55   $1,004.55   $1,004.70