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 $214.92   6.113%   $228.0581   $228.06   $228.05   $228.10  
  Purchase #2 $111.77   6.655%   $119.2083   $119.21   $119.20   $119.20  
  Purchase #3 $235.85   10.409%   $260.3996   $260.40   $260.40   $260.40  
  Purchase #4 $122.83   7.220%   $131.6983   $131.70   $131.70   $131.70  
  Purchase #5 $46.32   10.467%   $51.1683   $51.17   $51.15   $51.20  
  Purchase #6 $140.98   8.507%   $152.9732   $152.97   $152.95   $153.00  
  Purchase #7 $169.39   3.595%   $175.4796   $175.48   $175.50   $175.50  
  7 purchase totals = $1,042.06       $1,118.9854   $1,118.99   $1,118.95   $1,119.10