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 $162.33   13.724%   $184.6082   $184.61   $184.60   $184.60  
  Purchase #2 $177.81   3.241%   $183.5728   $183.57   $183.55   $183.60  
  Purchase #3 $135.66   4.315%   $141.5137   $141.51   $141.50   $141.50  
  Purchase #4 $65.88   13.655%   $74.8759   $74.88   $74.90   $74.90  
  Purchase #5 $43.97   10.684%   $48.6678   $48.67   $48.65   $48.70  
  Purchase #6 $118.57   10.282%   $130.7614   $130.76   $130.75   $130.80  
  Purchase #7 $235.75   8.431%   $255.6261   $255.63   $255.65   $255.60  
  7 purchase totals = $939.97       $1,019.6259   $1,019.63   $1,019.60   $1,019.70