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 $24.54   6.817%   $26.2129   $26.21   $26.20   $26.20  
  Purchase #2 $64.49   4.330%   $67.2824   $67.28   $67.30   $67.30  
  Purchase #3 $40.74   9.527%   $44.6213   $44.62   $44.60   $44.60  
  Purchase #4 $184.88   11.241%   $205.6624   $205.66   $205.65   $205.70  
  Purchase #5 $126.58   10.224%   $139.5215   $139.52   $139.50   $139.50  
  Purchase #6 $67.95   13.608%   $77.1966   $77.20   $77.20   $77.20  
  Purchase #7 $26.69   4.769%   $27.9628   $27.96   $27.95   $28.00  
  7 purchase totals = $535.87       $588.4599   $588.45   $588.40   $588.50