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 $241.32   8.122%   $260.92   $260.92   $260.90   $260.90  
  Purchase #2 $166.27   4.497%   $173.7472   $173.75   $173.75   $173.70  
  Purchase #3 $84.88   12.379%   $95.3873   $95.39   $95.40   $95.40  
  Purchase #4 $24.40   10.304%   $26.9142   $26.91   $26.90   $26.90  
  Purchase #5 $33.55   8.305%   $36.3363   $36.34   $36.35   $36.30  
  Purchase #6 $230.85   4.859%   $242.067   $242.07   $242.05   $242.10  
  Purchase #7 $18.82   6.208%   $19.9883   $19.99   $20.00   $20.00  
  7 purchase totals = $800.09       $855.3603   $855.37   $855.35   $855.30