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 $125.88   3.165%   $129.8641   $129.86   $129.85   $129.90  
  Purchase #2 $55.39   12.326%   $62.2174   $62.22   $62.20   $62.20  
  Purchase #3 $66.71   7.570%   $71.7599   $71.76   $71.75   $71.80  
  Purchase #4 $151.83   3.724%   $157.4841   $157.48   $157.50   $157.50  
  Purchase #5 $198.70   13.791%   $226.1027   $226.10   $226.10   $226.10  
  Purchase #6 $211.51   12.154%   $237.2169   $237.22   $237.20   $237.20  
  Purchase #7 $129.67   5.712%   $137.0768   $137.08   $137.10   $137.10  
  7 purchase totals = $939.69       $1,021.7219   $1,021.72   $1,021.70   $1,021.80