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 $183.63   13.137%   $207.7535   $207.75   $207.75   $207.80  
  Purchase #2 $149.46   7.407%   $160.5305   $160.53   $160.55   $160.50  
  Purchase #3 $24.63   6.724%   $26.2861   $26.29   $26.30   $26.30  
  Purchase #4 $176.81   10.868%   $196.0257   $196.03   $196.05   $196.00  
  Purchase #5 $83.82   4.793%   $87.8375   $87.84   $87.85   $87.80  
  Purchase #6 $198.42   13.587%   $225.3793   $225.38   $225.40   $225.40  
  Purchase #7 $52.97   8.112%   $57.2669   $57.27   $57.25   $57.30  
  7 purchase totals = $869.74       $961.0795   $961.09   $961.15   $961.10