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 $236.41   9.383%   $258.5924   $258.59   $258.60   $258.60  
  Purchase #2 $158.59   6.357%   $168.6716   $168.67   $168.65   $168.70  
  Purchase #3 $18.91   4.744%   $19.8071   $19.81   $19.80   $19.80  
  Purchase #4 $225.77   13.857%   $257.0549   $257.05   $257.05   $257.10  
  Purchase #5 $64.75   3.519%   $67.0286   $67.03   $67.05   $67.00  
  Purchase #6 $6.27   9.696%   $6.8779   $6.88   $6.90   $6.90  
  Purchase #7 $242.98   13.517%   $275.8236   $275.82   $275.80   $275.80  
  7 purchase totals = $953.68       $1,053.8561   $1,053.85   $1,053.85   $1,053.90