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 $119.30   4.216%   $124.3297   $124.33   $124.35   $124.30  
  Purchase #2 $145.28   9.591%   $159.2138   $159.21   $159.20   $159.20  
  Purchase #3 $157.60   13.618%   $179.062   $179.06   $179.05   $179.10  
  Purchase #4 $89.80   7.630%   $96.6517   $96.65   $96.65   $96.70  
  Purchase #5 $195.87   13.389%   $222.095   $222.10   $222.10   $222.10  
  Purchase #6 $50.86   3.386%   $52.5821   $52.58   $52.60   $52.60  
  Purchase #7 $224.77   12.602%   $253.0955   $253.10   $253.10   $253.10  
  7 purchase totals = $983.48       $1,087.0298   $1,087.03   $1,087.05   $1,087.10