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 $230.87   6.236%   $245.2671   $245.27   $245.25   $245.30  
  Purchase #2 $58.91   5.513%   $62.1577   $62.16   $62.15   $62.20  
  Purchase #3 $9.88   10.874%   $10.9544   $10.95   $10.95   $11.00  
  Purchase #4 $51.36   6.588%   $54.7436   $54.74   $54.75   $54.70  
  Purchase #5 $227.76   8.108%   $246.2268   $246.23   $246.25   $246.20  
  Purchase #6 $71.62   3.229%   $73.9326   $73.93   $73.95   $73.90  
  Purchase #7 $207.70   12.758%   $234.1984   $234.20   $234.20   $234.20  
  7 purchase totals = $858.10       $927.4806   $927.48   $927.50   $927.50