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 $64.62   13.432%   $73.2998   $73.30   $73.30   $73.30  
  Purchase #2 $104.92   6.219%   $111.445   $111.45   $111.45   $111.40  
  Purchase #3 $176.63   7.466%   $189.8172   $189.82   $189.80   $189.80  
  Purchase #4 $225.99   10.483%   $249.6805   $249.68   $249.70   $249.70  
  Purchase #5 $97.29   8.845%   $105.8953   $105.90   $105.90   $105.90  
  Purchase #6 $175.42   10.432%   $193.7198   $193.72   $193.70   $193.70  
  Purchase #7 $90.87   3.318%   $93.8851   $93.89   $93.90   $93.90  
  7 purchase totals = $935.74       $1,017.7427   $1,017.76   $1,017.75   $1,017.70