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 $62.68   5.604%   $66.1926   $66.19   $66.20   $66.20  
  Purchase #2 $47.56   13.695%   $54.0733   $54.07   $54.05   $54.10  
  Purchase #3 $201.91   13.248%   $228.659   $228.66   $228.65   $228.70  
  Purchase #4 $60.31   4.509%   $63.0294   $63.03   $63.05   $63.00  
  Purchase #5 $168.44   5.256%   $177.2932   $177.29   $177.30   $177.30  
  Purchase #6 $116.31   3.569%   $120.4611   $120.46   $120.45   $120.50  
  Purchase #7 $243.27   5.105%   $255.6889   $255.69   $255.70   $255.70  
  7 purchase totals = $900.48       $965.3975   $965.39   $965.40   $965.50