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 $134.93   12.370%   $151.6208   $151.62   $151.60   $151.60  
  Purchase #2 $174.81   9.564%   $191.5288   $191.53   $191.55   $191.50  
  Purchase #3 $79.55   7.538%   $85.5465   $85.55   $85.55   $85.50  
  Purchase #4 $58.35   10.852%   $64.6821   $64.68   $64.70   $64.70  
  Purchase #5 $92.94   5.325%   $97.8891   $97.89   $97.90   $97.90  
  Purchase #6 $24.51   6.633%   $26.1357   $26.14   $26.15   $26.10  
  Purchase #7 $157.25   7.220%   $168.6035   $168.60   $168.60   $168.60  
  7 purchase totals = $722.34       $786.0065   $786.01   $786.05   $785.90