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 $61.45   13.252%   $69.5934   $69.59   $69.60   $69.60  
  Purchase #2 $59.52   3.686%   $61.7139   $61.71   $61.70   $61.70  
  Purchase #3 $234.97   6.874%   $251.1218   $251.12   $251.10   $251.10  
  Purchase #4 $125.56   13.412%   $142.4001   $142.40   $142.40   $142.40  
  Purchase #5 $27.63   8.730%   $30.0421   $30.04   $30.05   $30.00  
  Purchase #6 $61.86   8.312%   $67.0018   $67.00   $67.00   $67.00  
  Purchase #7 $120.90   3.613%   $125.2681   $125.27   $125.25   $125.30  
  7 purchase totals = $691.89       $747.1412   $747.13   $747.10   $747.10