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 $149.66   8.495%   $162.3736   $162.37   $162.35   $162.40  
  Purchase #2 $201.61   6.608%   $214.9324   $214.93   $214.95   $214.90  
  Purchase #3 $68.84   7.131%   $73.749   $73.75   $73.75   $73.70  
  Purchase #4 $157.87   9.546%   $172.9403   $172.94   $172.95   $172.90  
  Purchase #5 $239.43   12.285%   $268.844   $268.84   $268.85   $268.80  
  Purchase #6 $229.65   8.368%   $248.8671   $248.87   $248.85   $248.90  
  Purchase #7 $111.87   3.769%   $116.0864   $116.09   $116.10   $116.10  
  7 purchase totals = $1,158.93       $1,257.7928   $1,257.79   $1,257.80   $1,257.70