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 $69.80   9.678%   $76.5552   $76.56   $76.55   $76.60  
  Purchase #2 $37.82   6.587%   $40.3112   $40.31   $40.30   $40.30  
  Purchase #3 $180.26   12.796%   $203.3261   $203.33   $203.35   $203.30  
  Purchase #4 $193.50   6.293%   $205.677   $205.68   $205.70   $205.70  
  Purchase #5 $176.69   10.724%   $195.6382   $195.64   $195.65   $195.60  
  Purchase #6 $164.92   11.416%   $183.7473   $183.75   $183.75   $183.70  
  Purchase #7 $170.28   13.511%   $193.2865   $193.29   $193.30   $193.30  
  7 purchase totals = $993.27       $1,098.5415   $1,098.56   $1,098.60   $1,098.50