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 $100.78   11.289%   $112.1571   $112.16   $112.15   $112.20  
  Purchase #2 $223.92   3.340%   $231.3989   $231.40   $231.40   $231.40  
  Purchase #3 $126.44   8.250%   $136.8713   $136.87   $136.85   $136.90  
  Purchase #4 $37.61   12.558%   $42.3331   $42.33   $42.35   $42.30  
  Purchase #5 $12.63   7.776%   $13.6121   $13.61   $13.60   $13.60  
  Purchase #6 $202.78   12.182%   $227.4827   $227.48   $227.50   $227.50  
  Purchase #7 $202.91   11.505%   $226.2548   $226.25   $226.25   $226.30  
  7 purchase totals = $907.07       $990.1100   $990.10   $990.10   $990.20