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 $249.95   5.122%   $262.7524   $262.75   $262.75   $262.80  
  Purchase #2 $242.69   9.359%   $265.4034   $265.40   $265.40   $265.40  
  Purchase #3 $35.67   4.466%   $37.263   $37.26   $37.25   $37.30  
  Purchase #4 $233.67   12.660%   $263.2526   $263.25   $263.25   $263.30  
  Purchase #5 $185.39   4.108%   $193.0058   $193.01   $193.00   $193.00  
  Purchase #6 $217.96   13.120%   $246.5564   $246.56   $246.55   $246.60  
  Purchase #7 $200.78   10.597%   $222.0567   $222.06   $222.05   $222.10  
  7 purchase totals = $1,366.11       $1,490.2903   $1,490.29   $1,490.25   $1,490.50