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 $59.84   4.710%   $62.6585   $62.66   $62.65   $62.70  
  Purchase #2 $158.52   11.814%   $177.2476   $177.25   $177.25   $177.20  
  Purchase #3 $15.76   7.646%   $16.965   $16.97   $16.95   $17.00  
  Purchase #4 $5.57   10.220%   $6.1393   $6.14   $6.15   $6.10  
  Purchase #5 $124.72   9.716%   $136.8378   $136.84   $136.85   $136.80  
  Purchase #6 $33.98   4.792%   $35.6083   $35.61   $35.60   $35.60  
  Purchase #7 $21.44   5.541%   $22.628   $22.63   $22.65   $22.60  
  7 purchase totals = $419.83       $458.0845   $458.10   $458.10   $458.00