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 $222.79   6.342%   $236.9193   $236.92   $236.90   $236.90  
  Purchase #2 $56.89   8.632%   $61.8007   $61.80   $61.80   $61.80  
  Purchase #3 $8.61   7.150%   $9.2256   $9.23   $9.25   $9.20  
  Purchase #4 $24.25   10.626%   $26.8268   $26.83   $26.85   $26.80  
  Purchase #5 $117.75   8.377%   $127.6139   $127.61   $127.60   $127.60  
  Purchase #6 $220.30   11.615%   $245.8878   $245.89   $245.90   $245.90  
  Purchase #7 $62.70   5.391%   $66.0802   $66.08   $66.10   $66.10  
  7 purchase totals = $713.29       $774.3543   $774.36   $774.40   $774.30