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 $29.42   10.757%   $32.5847   $32.58   $32.60   $32.60  
  Purchase #2 $14.89   5.479%   $15.7058   $15.71   $15.70   $15.70  
  Purchase #3 $216.68   11.397%   $241.375   $241.38   $241.40   $241.40  
  Purchase #4 $166.93   4.806%   $174.9527   $174.95   $174.95   $175.00  
  Purchase #5 $64.52   7.777%   $69.5377   $69.54   $69.55   $69.50  
  Purchase #6 $207.69   7.581%   $223.435   $223.44   $223.45   $223.40  
  Purchase #7 $191.93   11.874%   $214.7198   $214.72   $214.70   $214.70  
  7 purchase totals = $892.06       $972.3107   $972.32   $972.35   $972.30