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 $59.74   5.316%   $62.9158   $62.92   $62.90   $62.90  
  Purchase #2 $155.55   4.281%   $162.2091   $162.21   $162.20   $162.20  
  Purchase #3 $198.64   3.492%   $205.5765   $205.58   $205.60   $205.60  
  Purchase #4 $61.62   7.214%   $66.0653   $66.07   $66.05   $66.10  
  Purchase #5 $5.81   7.673%   $6.2558   $6.26   $6.25   $6.30  
  Purchase #6 $164.68   6.807%   $175.8898   $175.89   $175.90   $175.90  
  Purchase #7 $47.48   7.641%   $51.1079   $51.11   $51.10   $51.10  
  7 purchase totals = $693.52       $730.0202   $730.04   $730.00   $730.10