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 $246.74   6.435%   $262.6177   $262.62   $262.60   $262.60  
  Purchase #2 $175.98   7.322%   $188.8653   $188.87   $188.85   $188.90  
  Purchase #3 $13.48   13.109%   $15.2471   $15.25   $15.25   $15.20  
  Purchase #4 $38.71   9.477%   $42.3785   $42.38   $42.40   $42.40  
  Purchase #5 $136.84   10.115%   $150.6814   $150.68   $150.70   $150.70  
  Purchase #6 $191.64   5.759%   $202.6765   $202.68   $202.70   $202.70  
  Purchase #7 $128.85   7.366%   $138.3411   $138.34   $138.35   $138.30  
  7 purchase totals = $932.24       $1,000.8076   $1,000.82   $1,000.85   $1,000.80