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 $47.65   6.326%   $50.6643   $50.66   $50.65   $50.70  
  Purchase #2 $109.62   5.493%   $115.6414   $115.64   $115.65   $115.60  
  Purchase #3 $100.44   4.726%   $105.1868   $105.19   $105.20   $105.20  
  Purchase #4 $166.94   5.566%   $176.2319   $176.23   $176.25   $176.20  
  Purchase #5 $41.72   5.805%   $44.1418   $44.14   $44.15   $44.10  
  Purchase #6 $241.68   8.203%   $261.505   $261.51   $261.50   $261.50  
  Purchase #7 $30.50   8.474%   $33.0846   $33.08   $33.10   $33.10  
  7 purchase totals = $738.55       $786.4558   $786.45   $786.50   $786.40