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 $61.82   8.837%   $67.283   $67.28   $67.30   $67.30  
  Purchase #2 $214.47   5.221%   $225.6675   $225.67   $225.65   $225.70  
  Purchase #3 $152.41   10.325%   $168.1463   $168.15   $168.15   $168.10  
  Purchase #4 $106.50   12.310%   $119.6102   $119.61   $119.60   $119.60  
  Purchase #5 $88.34   12.326%   $99.2288   $99.23   $99.25   $99.20  
  Purchase #6 $125.95   9.795%   $138.2868   $138.29   $138.30   $138.30  
  Purchase #7 $221.76   7.197%   $237.7201   $237.72   $237.70   $237.70  
  7 purchase totals = $971.25       $1,055.9427   $1,055.95   $1,055.95   $1,055.90