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 $242.48   10.846%   $268.7794   $268.78   $268.80   $268.80  
  Purchase #2 $244.62   3.379%   $252.8857   $252.89   $252.90   $252.90  
  Purchase #3 $153.69   6.197%   $163.2142   $163.21   $163.20   $163.20  
  Purchase #4 $130.47   7.124%   $139.7647   $139.76   $139.75   $139.80  
  Purchase #5 $68.52   9.337%   $74.9177   $74.92   $74.90   $74.90  
  Purchase #6 $182.93   9.407%   $200.1382   $200.14   $200.15   $200.10  
  Purchase #7 $233.75   11.316%   $260.2012   $260.20   $260.20   $260.20  
  7 purchase totals = $1,256.46       $1,359.9011   $1,359.90   $1,359.90   $1,359.90