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 $24.74   6.159%   $26.2637   $26.26   $26.25   $26.30  
  Purchase #2 $187.66   3.689%   $194.5828   $194.58   $194.60   $194.60  
  Purchase #3 $71.71   6.168%   $76.1331   $76.13   $76.15   $76.10  
  Purchase #4 $164.87   12.559%   $185.576   $185.58   $185.60   $185.60  
  Purchase #5 $195.76   10.548%   $216.4088   $216.41   $216.40   $216.40  
  Purchase #6 $218.27   6.326%   $232.0778   $232.08   $232.10   $232.10  
  Purchase #7 $11.25   13.750%   $12.7969   $12.80   $12.80   $12.80  
  7 purchase totals = $874.26       $943.8391   $943.84   $943.90   $943.90