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 $182.69   7.796%   $196.9325   $196.93   $196.95   $196.90  
  Purchase #2 $100.27   13.858%   $114.1654   $114.17   $114.15   $114.20  
  Purchase #3 $120.75   11.116%   $134.1726   $134.17   $134.15   $134.20  
  Purchase #4 $184.79   9.331%   $202.0328   $202.03   $202.05   $202.00  
  Purchase #5 $57.49   10.378%   $63.4563   $63.46   $63.45   $63.50  
  Purchase #6 $146.35   4.754%   $153.3075   $153.31   $153.30   $153.30  
  Purchase #7 $106.81   11.352%   $118.9351   $118.94   $118.95   $118.90  
  7 purchase totals = $899.15       $983.0022   $983.01   $983.00   $983.00