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 $226.66   10.303%   $250.0128   $250.01   $250.00   $250.00  
  Purchase #2 $154.26   6.668%   $164.5461   $164.55   $164.55   $164.50  
  Purchase #3 $118.56   8.619%   $128.7787   $128.78   $128.80   $128.80  
  Purchase #4 $102.77   4.663%   $107.5622   $107.56   $107.55   $107.60  
  Purchase #5 $162.69   6.414%   $173.1249   $173.12   $173.10   $173.10  
  Purchase #6 $246.81   8.346%   $267.4088   $267.41   $267.40   $267.40  
  Purchase #7 $208.61   11.693%   $233.0028   $233.00   $233.00   $233.00  
  7 purchase totals = $1,220.36       $1,324.4363   $1,324.43   $1,324.40   $1,324.40