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 $207.51   6.546%   $221.0936   $221.09   $221.10   $221.10  
  Purchase #2 $183.69   7.289%   $197.0792   $197.08   $197.10   $197.10  
  Purchase #3 $55.51   11.131%   $61.6888   $61.69   $61.70   $61.70  
  Purchase #4 $154.33   4.724%   $161.6205   $161.62   $161.60   $161.60  
  Purchase #5 $192.40   11.172%   $213.8949   $213.89   $213.90   $213.90  
  Purchase #6 $197.90   11.592%   $220.8406   $220.84   $220.85   $220.80  
  Purchase #7 $167.74   5.514%   $176.9892   $176.99   $177.00   $177.00  
  7 purchase totals = $1,159.08       $1,253.2068   $1,253.20   $1,253.25   $1,253.20