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 $51.44   10.341%   $56.7594   $56.76   $56.75   $56.80  
  Purchase #2 $102.37   7.815%   $110.3702   $110.37   $110.35   $110.40  
  Purchase #3 $101.67   12.705%   $114.5872   $114.59   $114.60   $114.60  
  Purchase #4 $231.77   4.684%   $242.6261   $242.63   $242.65   $242.60  
  Purchase #5 $167.64   4.153%   $174.6021   $174.60   $174.60   $174.60  
  Purchase #6 $135.25   5.392%   $142.5427   $142.54   $142.55   $142.50  
  Purchase #7 $192.30   12.289%   $215.9317   $215.93   $215.95   $215.90  
  7 purchase totals = $982.44       $1,057.4194   $1,057.42   $1,057.45   $1,057.40