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 $180.27   13.523%   $204.6479   $204.65   $204.65   $204.60  
  Purchase #2 $33.95   9.424%   $37.1494   $37.15   $37.15   $37.10  
  Purchase #3 $10.72   11.874%   $11.9929   $11.99   $12.00   $12.00  
  Purchase #4 $185.51   11.873%   $207.5356   $207.54   $207.55   $207.50  
  Purchase #5 $52.60   10.748%   $58.2534   $58.25   $58.25   $58.30  
  Purchase #6 $166.35   7.416%   $178.6865   $178.69   $178.70   $178.70  
  Purchase #7 $235.84   4.174%   $245.684   $245.68   $245.70   $245.70  
  7 purchase totals = $865.24       $943.9497   $943.95   $944.00   $943.90