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 $144.65   12.379%   $162.5562   $162.56   $162.55   $162.60  
  Purchase #2 $123.42   9.147%   $134.7092   $134.71   $134.70   $134.70  
  Purchase #3 $247.56   7.678%   $266.5677   $266.57   $266.55   $266.60  
  Purchase #4 $149.76   12.554%   $168.5609   $168.56   $168.55   $168.60  
  Purchase #5 $208.59   12.615%   $234.9036   $234.90   $234.90   $234.90  
  Purchase #6 $151.51   6.691%   $161.6475   $161.65   $161.65   $161.60  
  Purchase #7 $141.30   11.142%   $157.0436   $157.04   $157.05   $157.00  
  7 purchase totals = $1,166.79       $1,285.9887   $1,285.99   $1,285.95   $1,286.00