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 $250.77   10.151%   $276.2257   $276.23   $276.25   $276.20  
  Purchase #2 $245.39   13.137%   $277.6269   $277.63   $277.65   $277.60  
  Purchase #3 $68.76   11.466%   $76.644   $76.64   $76.65   $76.60  
  Purchase #4 $227.48   11.775%   $254.2658   $254.27   $254.25   $254.30  
  Purchase #5 $76.96   3.610%   $79.7383   $79.74   $79.75   $79.70  
  Purchase #6 $94.68   6.579%   $100.909   $100.91   $100.90   $100.90  
  Purchase #7 $26.85   12.816%   $30.2911   $30.29   $30.30   $30.30  
  7 purchase totals = $990.89       $1,095.7008   $1,095.71   $1,095.75   $1,095.60