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 $126.92   8.346%   $137.5127   $137.51   $137.50   $137.50  
  Purchase #2 $108.65   6.279%   $115.4721   $115.47   $115.45   $115.50  
  Purchase #3 $230.74   12.675%   $259.9863   $259.99   $260.00   $260.00  
  Purchase #4 $61.40   5.257%   $64.6278   $64.63   $64.65   $64.60  
  Purchase #5 $208.87   13.365%   $236.7855   $236.79   $236.80   $236.80  
  Purchase #6 $154.40   12.849%   $174.2389   $174.24   $174.25   $174.20  
  Purchase #7 $24.34   7.262%   $26.1076   $26.11   $26.10   $26.10  
  7 purchase totals = $915.32       $1,014.7309   $1,014.74   $1,014.75   $1,014.70