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 $36.68   12.698%   $41.3376   $41.34   $41.35   $41.30  
  Purchase #2 $124.51   9.308%   $136.0994   $136.10   $136.10   $136.10  
  Purchase #3 $154.64   5.574%   $163.2596   $163.26   $163.25   $163.30  
  Purchase #4 $247.41   6.256%   $262.888   $262.89   $262.90   $262.90  
  Purchase #5 $232.96   7.142%   $249.598   $249.60   $249.60   $249.60  
  Purchase #6 $128.63   8.141%   $139.1018   $139.10   $139.10   $139.10  
  Purchase #7 $170.58   9.743%   $187.1996   $187.20   $187.20   $187.20  
  7 purchase totals = $1,095.41       $1,179.4840   $1,179.49   $1,179.50   $1,179.50