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 $238.92   12.780%   $269.454   $269.45   $269.45   $269.50  
  Purchase #2 $8.99   7.532%   $9.6671   $9.67   $9.65   $9.70  
  Purchase #3 $184.78   12.584%   $208.0327   $208.03   $208.05   $208.00  
  Purchase #4 $126.97   7.262%   $136.1906   $136.19   $136.20   $136.20  
  Purchase #5 $157.71   10.383%   $174.085   $174.09   $174.10   $174.10  
  Purchase #6 $162.62   10.158%   $179.1389   $179.14   $179.15   $179.10  
  Purchase #7 $66.56   13.645%   $75.6421   $75.64   $75.65   $75.60  
  7 purchase totals = $946.55       $1,052.2104   $1,052.21   $1,052.25   $1,052.20