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 $57.93   3.543%   $59.9825   $59.98   $60.00   $60.00  
  Purchase #2 $111.35   6.669%   $118.7759   $118.78   $118.80   $118.80  
  Purchase #3 $153.83   13.741%   $174.9678   $174.97   $174.95   $175.00  
  Purchase #4 $163.78   7.453%   $175.9865   $175.99   $176.00   $176.00  
  Purchase #5 $146.61   7.407%   $157.4694   $157.47   $157.45   $157.50  
  Purchase #6 $56.55   8.282%   $61.2335   $61.23   $61.25   $61.20  
  Purchase #7 $191.80   8.331%   $207.7789   $207.78   $207.80   $207.80  
  7 purchase totals = $881.85       $956.1945   $956.20   $956.25   $956.30