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 $250.25   6.267%   $265.9332   $265.93   $265.95   $265.90  
  Purchase #2 $126.58   12.724%   $142.686   $142.69   $142.70   $142.70  
  Purchase #3 $220.62   6.747%   $235.5052   $235.51   $235.50   $235.50  
  Purchase #4 $88.68   7.298%   $95.1519   $95.15   $95.15   $95.20  
  Purchase #5 $159.87   6.847%   $170.8163   $170.82   $170.80   $170.80  
  Purchase #6 $154.79   5.516%   $163.3282   $163.33   $163.35   $163.30  
  Purchase #7 $121.82   8.270%   $131.8945   $131.89   $131.90   $131.90  
  7 purchase totals = $1,122.61       $1,205.3153   $1,205.32   $1,205.35   $1,205.30