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 $30.78   5.659%   $32.5218   $32.52   $32.50   $32.50  
  Purchase #2 $22.34   3.153%   $23.0444   $23.04   $23.05   $23.00  
  Purchase #3 $95.76   9.357%   $104.7203   $104.72   $104.70   $104.70  
  Purchase #4 $65.71   7.595%   $70.7007   $70.70   $70.70   $70.70  
  Purchase #5 $167.41   9.470%   $183.2637   $183.26   $183.25   $183.30  
  Purchase #6 $143.67   12.302%   $161.3443   $161.34   $161.35   $161.30  
  Purchase #7 $105.88   10.694%   $117.2028   $117.20   $117.20   $117.20  
  7 purchase totals = $631.55       $692.7980   $692.78   $692.75   $692.70