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 $72.49   12.754%   $81.7354   $81.74   $81.75   $81.70  
  Purchase #2 $171.43   6.420%   $182.4358   $182.44   $182.45   $182.40  
  Purchase #3 $234.49   8.329%   $254.0207   $254.02   $254.00   $254.00  
  Purchase #4 $114.60   10.696%   $126.8576   $126.86   $126.85   $126.90  
  Purchase #5 $187.74   13.241%   $212.5987   $212.60   $212.60   $212.60  
  Purchase #6 $144.78   12.752%   $163.2423   $163.24   $163.25   $163.20  
  Purchase #7 $87.92   8.530%   $95.4196   $95.42   $95.40   $95.40  
  7 purchase totals = $1,013.45       $1,116.3101   $1,116.32   $1,116.30   $1,116.20