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 $5.40   8.858%   $5.8783   $5.88   $5.90   $5.90  
  Purchase #2 $49.72   6.650%   $53.0264   $53.03   $53.05   $53.00  
  Purchase #3 $145.58   12.325%   $163.5227   $163.52   $163.50   $163.50  
  Purchase #4 $242.55   11.782%   $271.1272   $271.13   $271.15   $271.10  
  Purchase #5 $197.60   5.564%   $208.5945   $208.59   $208.60   $208.60  
  Purchase #6 $21.25   6.708%   $22.6755   $22.68   $22.70   $22.70  
  Purchase #7 $233.70   8.228%   $252.9288   $252.93   $252.95   $252.90  
  7 purchase totals = $895.80       $977.7534   $977.76   $977.85   $977.70