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 $250.64   6.113%   $265.9616   $265.96   $265.95   $266.00  
  Purchase #2 $185.99   8.757%   $202.2771   $202.28   $202.30   $202.30  
  Purchase #3 $223.56   8.678%   $242.9605   $242.96   $242.95   $243.00  
  Purchase #4 $56.49   13.655%   $64.2037   $64.20   $64.20   $64.20  
  Purchase #5 $108.91   7.490%   $117.0674   $117.07   $117.05   $117.10  
  Purchase #6 $231.40   5.427%   $243.9581   $243.96   $243.95   $244.00  
  Purchase #7 $208.82   7.157%   $223.7652   $223.77   $223.75   $223.80  
  7 purchase totals = $1,265.81       $1,360.1936   $1,360.20   $1,360.15   $1,360.40