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 $81.55   12.304%   $91.5839   $91.58   $91.60   $91.60  
  Purchase #2 $114.72   7.283%   $123.0751   $123.08   $123.10   $123.10  
  Purchase #3 $175.79   4.614%   $183.901   $183.90   $183.90   $183.90  
  Purchase #4 $239.53   8.702%   $260.3739   $260.37   $260.35   $260.40  
  Purchase #5 $51.33   7.593%   $55.2275   $55.23   $55.25   $55.20  
  Purchase #6 $235.63   5.241%   $247.9794   $247.98   $248.00   $248.00  
  Purchase #7 $211.76   13.246%   $239.8097   $239.81   $239.80   $239.80  
  7 purchase totals = $1,110.31       $1,201.9505   $1,201.95   $1,202.00   $1,202.00