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 $24.77   12.503%   $27.867   $27.87   $27.85   $27.90  
  Purchase #2 $106.95   6.154%   $113.5317   $113.53   $113.55   $113.50  
  Purchase #3 $12.80   5.539%   $13.509   $13.51   $13.50   $13.50  
  Purchase #4 $96.67   6.171%   $102.6355   $102.64   $102.65   $102.60  
  Purchase #5 $205.57   5.762%   $217.4149   $217.41   $217.40   $217.40  
  Purchase #6 $97.70   8.605%   $106.1071   $106.11   $106.10   $106.10  
  Purchase #7 $195.36   6.482%   $208.0232   $208.02   $208.00   $208.00  
  7 purchase totals = $739.82       $789.0884   $789.09   $789.05   $789.00