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 $222.44   10.478%   $245.7473   $245.75   $245.75   $245.70  
  Purchase #2 $61.37   13.536%   $69.677   $69.68   $69.70   $69.70  
  Purchase #3 $61.39   5.527%   $64.783   $64.78   $64.80   $64.80  
  Purchase #4 $237.92   8.696%   $258.6095   $258.61   $258.60   $258.60  
  Purchase #5 $243.94   9.628%   $267.4265   $267.43   $267.45   $267.40  
  Purchase #6 $222.63   13.354%   $252.36   $252.36   $252.35   $252.40  
  Purchase #7 $56.54   11.196%   $62.8702   $62.87   $62.85   $62.90  
  7 purchase totals = $1,106.23       $1,221.4735   $1,221.48   $1,221.50   $1,221.50