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 $191.94   11.771%   $214.5333   $214.53   $214.55   $214.50  
  Purchase #2 $76.74   10.498%   $84.7962   $84.80   $84.80   $84.80  
  Purchase #3 $153.81   10.169%   $169.4509   $169.45   $169.45   $169.50  
  Purchase #4 $73.73   6.230%   $78.3234   $78.32   $78.30   $78.30  
  Purchase #5 $126.31   8.388%   $136.9049   $136.90   $136.90   $136.90  
  Purchase #6 $169.28   4.861%   $177.5087   $177.51   $177.50   $177.50  
  Purchase #7 $5.34   9.476%   $5.846   $5.85   $5.85   $5.80  
  7 purchase totals = $797.15       $867.3634   $867.36   $867.35   $867.30