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 $106.64   12.200%   $119.6501   $119.65   $119.65   $119.70  
  Purchase #2 $21.29   9.306%   $23.2712   $23.27   $23.25   $23.30  
  Purchase #3 $183.53   8.275%   $198.7171   $198.72   $198.70   $198.70  
  Purchase #4 $59.92   13.294%   $67.8858   $67.89   $67.90   $67.90  
  Purchase #5 $67.95   11.651%   $75.8669   $75.87   $75.85   $75.90  
  Purchase #6 $27.59   7.325%   $29.611   $29.61   $29.60   $29.60  
  Purchase #7 $208.97   8.755%   $227.2653   $227.27   $227.25   $227.30  
  7 purchase totals = $675.89       $742.2674   $742.28   $742.20   $742.40