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 $147.35   5.299%   $155.1581   $155.16   $155.15   $155.20  
  Purchase #2 $127.83   5.148%   $134.4107   $134.41   $134.40   $134.40  
  Purchase #3 $122.66   11.841%   $137.1842   $137.18   $137.20   $137.20  
  Purchase #4 $191.50   8.767%   $208.2888   $208.29   $208.30   $208.30  
  Purchase #5 $246.52   7.327%   $264.5825   $264.58   $264.60   $264.60  
  Purchase #6 $69.97   3.540%   $72.4469   $72.45   $72.45   $72.40  
  Purchase #7 $46.25   12.150%   $51.8694   $51.87   $51.85   $51.90  
  7 purchase totals = $952.08       $1,023.9406   $1,023.94   $1,023.95   $1,024.00