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 $5.28   13.554%   $5.9957   $6.00   $6.00   $6.00  
  Purchase #2 $208.77   8.336%   $226.1731   $226.17   $226.15   $226.20  
  Purchase #3 $227.71   12.731%   $256.6998   $256.70   $256.70   $256.70  
  Purchase #4 $97.83   3.304%   $101.0623   $101.06   $101.05   $101.10  
  Purchase #5 $223.37   12.220%   $250.6658   $250.67   $250.65   $250.70  
  Purchase #6 $119.68   3.848%   $124.2853   $124.29   $124.30   $124.30  
  Purchase #7 $43.99   12.207%   $49.3599   $49.36   $49.35   $49.40  
  7 purchase totals = $926.63       $1,014.2419   $1,014.25   $1,014.20   $1,014.40