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 $185.78   9.326%   $203.1058   $203.11   $203.10   $203.10  
  Purchase #2 $56.36   11.141%   $62.6391   $62.64   $62.65   $62.60  
  Purchase #3 $182.88   4.714%   $191.501   $191.50   $191.50   $191.50  
  Purchase #4 $170.45   10.246%   $187.9143   $187.91   $187.90   $187.90  
  Purchase #5 $161.95   5.525%   $170.8977   $170.90   $170.90   $170.90  
  Purchase #6 $239.55   8.106%   $258.9679   $258.97   $258.95   $259.00  
  Purchase #7 $234.62   9.847%   $257.723   $257.72   $257.70   $257.70  
  7 purchase totals = $1,231.59       $1,332.7488   $1,332.75   $1,332.70   $1,332.70