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 $89.66   4.756%   $93.9242   $93.92   $93.90   $93.90  
  Purchase #2 $239.41   11.197%   $266.2167   $266.22   $266.20   $266.20  
  Purchase #3 $68.92   12.746%   $77.7045   $77.70   $77.70   $77.70  
  Purchase #4 $172.59   12.582%   $194.3053   $194.31   $194.30   $194.30  
  Purchase #5 $142.46   11.185%   $158.3942   $158.39   $158.40   $158.40  
  Purchase #6 $198.81   6.825%   $212.3788   $212.38   $212.40   $212.40  
  Purchase #7 $185.37   8.702%   $201.5009   $201.50   $201.50   $201.50  
  7 purchase totals = $1,097.22       $1,204.4246   $1,204.42   $1,204.40   $1,204.40