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 $105.64   13.366%   $119.7598   $119.76   $119.75   $119.80  
  Purchase #2 $153.86   8.270%   $166.5842   $166.58   $166.60   $166.60  
  Purchase #3 $210.35   5.826%   $222.605   $222.61   $222.60   $222.60  
  Purchase #4 $232.77   9.163%   $254.0987   $254.10   $254.10   $254.10  
  Purchase #5 $74.35   13.826%   $84.6296   $84.63   $84.65   $84.60  
  Purchase #6 $25.48   5.714%   $26.9359   $26.94   $26.95   $26.90  
  Purchase #7 $217.50   5.825%   $230.1694   $230.17   $230.15   $230.20  
  7 purchase totals = $1,019.95       $1,104.7826   $1,104.79   $1,104.80   $1,104.80