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 $142.72   13.125%   $161.452   $161.45   $161.45   $161.50  
  Purchase #2 $129.98   5.465%   $137.0834   $137.08   $137.10   $137.10  
  Purchase #3 $113.84   8.119%   $123.0827   $123.08   $123.10   $123.10  
  Purchase #4 $8.78   13.807%   $9.9923   $9.99   $10.00   $10.00  
  Purchase #5 $189.46   9.835%   $208.0934   $208.09   $208.10   $208.10  
  Purchase #6 $121.66   8.391%   $131.8685   $131.87   $131.85   $131.90  
  Purchase #7 $178.33   11.374%   $198.6133   $198.61   $198.60   $198.60  
  7 purchase totals = $884.77       $970.1856   $970.17   $970.20   $970.30