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 $123.81   8.866%   $134.787   $134.79   $134.80   $134.80  
  Purchase #2 $56.42   8.395%   $61.1565   $61.16   $61.15   $61.20  
  Purchase #3 $77.70   6.364%   $82.6448   $82.64   $82.65   $82.60  
  Purchase #4 $131.77   9.509%   $144.3   $144.30   $144.30   $144.30  
  Purchase #5 $154.81   13.592%   $175.8518   $175.85   $175.85   $175.90  
  Purchase #6 $213.61   6.141%   $226.7278   $226.73   $226.75   $226.70  
  Purchase #7 $117.99   11.325%   $131.3524   $131.35   $131.35   $131.40  
  7 purchase totals = $876.11       $956.8203   $956.82   $956.85   $956.90