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 $217.81   6.426%   $231.8065   $231.81   $231.80   $231.80  
  Purchase #2 $150.65   8.872%   $164.0157   $164.02   $164.00   $164.00  
  Purchase #3 $116.82   5.780%   $123.5722   $123.57   $123.55   $123.60  
  Purchase #4 $60.37   9.531%   $66.1239   $66.12   $66.10   $66.10  
  Purchase #5 $140.87   11.602%   $157.2137   $157.21   $157.20   $157.20  
  Purchase #6 $191.61   7.786%   $206.5288   $206.53   $206.55   $206.50  
  Purchase #7 $117.50   5.754%   $124.261   $124.26   $124.25   $124.30  
  7 purchase totals = $995.63       $1,073.5218   $1,073.52   $1,073.45   $1,073.50