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 $206.64   13.542%   $234.6232   $234.62   $234.60   $234.60  
  Purchase #2 $175.26   7.214%   $187.9033   $187.90   $187.90   $187.90  
  Purchase #3 $237.25   3.678%   $245.9761   $245.98   $246.00   $246.00  
  Purchase #4 $90.31   6.207%   $95.9155   $95.92   $95.90   $95.90  
  Purchase #5 $202.47   11.653%   $226.0638   $226.06   $226.05   $226.10  
  Purchase #6 $114.88   13.802%   $130.7357   $130.74   $130.75   $130.70  
  Purchase #7 $219.35   6.493%   $233.5924   $233.59   $233.60   $233.60  
  7 purchase totals = $1,246.16       $1,354.8100   $1,354.81   $1,354.80   $1,354.80