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 $86.61   11.528%   $96.5944   $96.59   $96.60   $96.60  
  Purchase #2 $85.83   3.622%   $88.9388   $88.94   $88.95   $88.90  
  Purchase #3 $9.62   3.544%   $9.9609   $9.96   $9.95   $10.00  
  Purchase #4 $214.93   7.656%   $231.385   $231.39   $231.40   $231.40  
  Purchase #5 $127.59   6.553%   $135.951   $135.95   $135.95   $136.00  
  Purchase #6 $236.30   13.320%   $267.7752   $267.78   $267.80   $267.80  
  Purchase #7 $115.94   12.591%   $130.538   $130.54   $130.55   $130.50  
  7 purchase totals = $876.82       $961.1433   $961.15   $961.20   $961.20