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 $241.30   11.701%   $269.5345   $269.53   $269.55   $269.50  
  Purchase #2 $158.32   13.151%   $179.1407   $179.14   $179.15   $179.10  
  Purchase #3 $117.68   13.608%   $133.6939   $133.69   $133.70   $133.70  
  Purchase #4 $213.43   12.763%   $240.6701   $240.67   $240.65   $240.70  
  Purchase #5 $235.33   5.436%   $248.1225   $248.12   $248.10   $248.10  
  Purchase #6 $88.63   6.316%   $94.2279   $94.23   $94.25   $94.20  
  Purchase #7 $202.35   4.797%   $212.0567   $212.06   $212.05   $212.10  
  7 purchase totals = $1,257.04       $1,377.4463   $1,377.44   $1,377.45   $1,377.40