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 $65.90   11.684%   $73.5998   $73.60   $73.60   $73.60  
  Purchase #2 $238.34   6.590%   $254.0466   $254.05   $254.05   $254.00  
  Purchase #3 $178.88   5.458%   $188.6433   $188.64   $188.65   $188.60  
  Purchase #4 $179.25   10.558%   $198.1752   $198.18   $198.20   $198.20  
  Purchase #5 $122.72   11.351%   $136.6499   $136.65   $136.65   $136.60  
  Purchase #6 $131.47   13.621%   $149.3775   $149.38   $149.40   $149.40  
  Purchase #7 $46.94   5.355%   $49.4536   $49.45   $49.45   $49.50  
  7 purchase totals = $963.50       $1,049.9459   $1,049.95   $1,050.00   $1,049.90