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 $209.37   13.306%   $237.2288   $237.23   $237.25   $237.20  
  Purchase #2 $27.76   6.737%   $29.6302   $29.63   $29.65   $29.60  
  Purchase #3 $58.88   3.318%   $60.8336   $60.83   $60.85   $60.80  
  Purchase #4 $140.32   8.553%   $152.3216   $152.32   $152.30   $152.30  
  Purchase #5 $216.58   12.578%   $243.8214   $243.82   $243.80   $243.80  
  Purchase #6 $224.49   10.807%   $248.7506   $248.75   $248.75   $248.80  
  Purchase #7 $57.83   9.673%   $63.4239   $63.42   $63.40   $63.40  
  7 purchase totals = $935.23       $1,036.0101   $1,036.00   $1,036.00   $1,035.90