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 $239.49   5.231%   $252.0177   $252.02   $252.00   $252.00  
  Purchase #2 $246.43   3.298%   $254.5573   $254.56   $254.55   $254.60  
  Purchase #3 $66.64   3.266%   $68.8165   $68.82   $68.80   $68.80  
  Purchase #4 $193.97   3.175%   $200.1285   $200.13   $200.15   $200.10  
  Purchase #5 $161.83   11.587%   $180.5812   $180.58   $180.60   $180.60  
  Purchase #6 $217.69   5.866%   $230.4597   $230.46   $230.45   $230.50  
  Purchase #7 $26.31   7.724%   $28.3422   $28.34   $28.35   $28.30  
  7 purchase totals = $1,152.36       $1,214.9031   $1,214.91   $1,214.90   $1,214.90