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 $43.64   13.775%   $49.6514   $49.65   $49.65   $49.70  
  Purchase #2 $113.44   5.342%   $119.5   $119.50   $119.50   $119.50  
  Purchase #3 $88.67   6.839%   $94.7341   $94.73   $94.75   $94.70  
  Purchase #4 $9.45   4.654%   $9.8898   $9.89   $9.90   $9.90  
  Purchase #5 $203.95   6.873%   $217.9675   $217.97   $217.95   $218.00  
  Purchase #6 $185.41   8.599%   $201.3534   $201.35   $201.35   $201.40  
  Purchase #7 $192.69   7.666%   $207.4616   $207.46   $207.45   $207.50  
  7 purchase totals = $837.25       $900.5578   $900.55   $900.55   $900.70