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 $209.67   12.712%   $236.3233   $236.32   $236.30   $236.30  
  Purchase #2 $41.46   13.211%   $46.9373   $46.94   $46.95   $46.90  
  Purchase #3 $110.86   5.371%   $116.8143   $116.81   $116.80   $116.80  
  Purchase #4 $25.33   4.214%   $26.3974   $26.40   $26.40   $26.40  
  Purchase #5 $149.29   9.116%   $162.8993   $162.90   $162.90   $162.90  
  Purchase #6 $49.64   4.563%   $51.9051   $51.91   $51.90   $51.90  
  Purchase #7 $186.91   3.685%   $193.7976   $193.80   $193.80   $193.80  
  7 purchase totals = $773.16       $835.0743   $835.08   $835.05   $835.00