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 $62.54   13.451%   $70.9523   $70.95   $70.95   $71.00  
  Purchase #2 $129.55   12.823%   $146.1622   $146.16   $146.15   $146.20  
  Purchase #3 $5.99   8.838%   $6.5194   $6.52   $6.50   $6.50  
  Purchase #4 $101.47   7.646%   $109.2284   $109.23   $109.25   $109.20  
  Purchase #5 $214.94   7.434%   $230.9186   $230.92   $230.90   $230.90  
  Purchase #6 $57.77   4.638%   $60.4494   $60.45   $60.45   $60.40  
  Purchase #7 $128.53   8.765%   $139.7957   $139.80   $139.80   $139.80  
  7 purchase totals = $700.79       $764.0260   $764.03   $764.00   $764.00