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 $206.98   8.783%   $225.1591   $225.16   $225.15   $225.20  
  Purchase #2 $206.63   11.391%   $230.1672   $230.17   $230.15   $230.20  
  Purchase #3 $68.69   11.718%   $76.7391   $76.74   $76.75   $76.70  
  Purchase #4 $89.98   5.615%   $95.0324   $95.03   $95.05   $95.00  
  Purchase #5 $64.61   13.537%   $73.3563   $73.36   $73.35   $73.40  
  Purchase #6 $249.89   3.540%   $258.7361   $258.74   $258.75   $258.70  
  Purchase #7 $68.90   8.550%   $74.791   $74.79   $74.80   $74.80  
  7 purchase totals = $955.68       $1,033.9812   $1,033.99   $1,034.00   $1,034.00