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 $232.33   6.166%   $246.6555   $246.66   $246.65   $246.70  
  Purchase #2 $224.63   5.204%   $236.3197   $236.32   $236.30   $236.30  
  Purchase #3 $77.80   13.191%   $88.0626   $88.06   $88.05   $88.10  
  Purchase #4 $30.28   7.758%   $32.6291   $32.63   $32.65   $32.60  
  Purchase #5 $175.32   9.193%   $191.4372   $191.44   $191.45   $191.40  
  Purchase #6 $184.70   6.491%   $196.6889   $196.69   $196.70   $196.70  
  Purchase #7 $136.94   11.746%   $153.025   $153.03   $153.05   $153.00  
  7 purchase totals = $1,062.00       $1,144.8180   $1,144.83   $1,144.85   $1,144.80