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 $71.28   6.156%   $75.668   $75.67   $75.65   $75.70  
  Purchase #2 $238.93   8.188%   $258.4936   $258.49   $258.50   $258.50  
  Purchase #3 $163.77   7.734%   $176.436   $176.44   $176.45   $176.40  
  Purchase #4 $25.44   10.336%   $28.0695   $28.07   $28.05   $28.10  
  Purchase #5 $133.61   10.422%   $147.5348   $147.53   $147.55   $147.50  
  Purchase #6 $115.86   3.283%   $119.6637   $119.66   $119.65   $119.70  
  Purchase #7 $203.85   9.512%   $223.2402   $223.24   $223.25   $223.20  
  7 purchase totals = $952.74       $1,029.1058   $1,029.10   $1,029.10   $1,029.10