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 $23.41   12.392%   $26.311   $26.31   $26.30   $26.30  
  Purchase #2 $226.47   8.246%   $245.1447   $245.14   $245.15   $245.10  
  Purchase #3 $39.96   6.300%   $42.4775   $42.48   $42.50   $42.50  
  Purchase #4 $100.44   10.461%   $110.947   $110.95   $110.95   $110.90  
  Purchase #5 $248.65   7.180%   $266.5031   $266.50   $266.50   $266.50  
  Purchase #6 $127.33   9.808%   $139.8185   $139.82   $139.80   $139.80  
  Purchase #7 $99.36   7.487%   $106.7991   $106.80   $106.80   $106.80  
  7 purchase totals = $865.62       $938.0009   $938.00   $938.00   $937.90