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 $177.85   13.441%   $201.7548   $201.75   $201.75   $201.80  
  Purchase #2 $57.83   9.339%   $63.2307   $63.23   $63.25   $63.20  
  Purchase #3 $136.41   11.218%   $151.7125   $151.71   $151.70   $151.70  
  Purchase #4 $122.69   10.220%   $135.2289   $135.23   $135.25   $135.20  
  Purchase #5 $136.27   3.722%   $141.342   $141.34   $141.35   $141.30  
  Purchase #6 $24.69   4.687%   $25.8472   $25.85   $25.85   $25.80  
  Purchase #7 $78.46   5.302%   $82.6199   $82.62   $82.60   $82.60  
  7 purchase totals = $734.20       $801.7360   $801.73   $801.75   $801.60