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 $208.78   7.117%   $223.6389   $223.64   $223.65   $223.60  
  Purchase #2 $92.66   8.600%   $100.6288   $100.63   $100.65   $100.60  
  Purchase #3 $161.38   9.274%   $176.3464   $176.35   $176.35   $176.30  
  Purchase #4 $93.78   5.209%   $98.665   $98.67   $98.65   $98.70  
  Purchase #5 $163.78   7.591%   $176.2125   $176.21   $176.20   $176.20  
  Purchase #6 $171.54   4.400%   $179.0878   $179.09   $179.10   $179.10  
  Purchase #7 $62.60   7.449%   $67.2631   $67.26   $67.25   $67.30  
  7 purchase totals = $954.52       $1,021.8425   $1,021.85   $1,021.85   $1,021.80