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 $56.97   9.252%   $62.2409   $62.24   $62.25   $62.20  
  Purchase #2 $68.95   11.574%   $76.9303   $76.93   $76.95   $76.90  
  Purchase #3 $235.52   6.436%   $250.6781   $250.68   $250.70   $250.70  
  Purchase #4 $201.98   9.857%   $221.8892   $221.89   $221.90   $221.90  
  Purchase #5 $239.95   8.590%   $260.5617   $260.56   $260.55   $260.60  
  Purchase #6 $60.83   3.644%   $63.0466   $63.05   $63.05   $63.00  
  Purchase #7 $69.51   3.838%   $72.1778   $72.18   $72.20   $72.20  
  7 purchase totals = $933.71       $1,007.5246   $1,007.53   $1,007.60   $1,007.50