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 $242.76   8.618%   $263.6811   $263.68   $263.70   $263.70  
  Purchase #2 $175.57   10.694%   $194.3455   $194.35   $194.35   $194.30  
  Purchase #3 $37.41   5.151%   $39.337   $39.34   $39.35   $39.30  
  Purchase #4 $104.87   5.301%   $110.4292   $110.43   $110.45   $110.40  
  Purchase #5 $142.41   6.601%   $151.8105   $151.81   $151.80   $151.80  
  Purchase #6 $227.72   6.787%   $243.1754   $243.18   $243.20   $243.20  
  Purchase #7 $21.30   8.218%   $23.0504   $23.05   $23.05   $23.10  
  7 purchase totals = $952.04       $1,025.8291   $1,025.84   $1,025.90   $1,025.80