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 $52.39   8.834%   $57.0181   $57.02   $57.00   $57.00  
  Purchase #2 $97.38   13.504%   $110.5302   $110.53   $110.55   $110.50  
  Purchase #3 $69.94   9.509%   $76.5906   $76.59   $76.60   $76.60  
  Purchase #4 $230.91   13.524%   $262.1383   $262.14   $262.15   $262.10  
  Purchase #5 $108.97   6.210%   $115.737   $115.74   $115.75   $115.70  
  Purchase #6 $74.97   12.346%   $84.2258   $84.23   $84.25   $84.20  
  Purchase #7 $167.40   8.246%   $181.2038   $181.20   $181.20   $181.20  
  7 purchase totals = $801.96       $887.4438   $887.45   $887.50   $887.30