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 $24.61   7.517%   $26.4599   $26.46   $26.45   $26.50  
  Purchase #2 $167.67   8.303%   $181.5916   $181.59   $181.60   $181.60  
  Purchase #3 $51.44   6.518%   $54.7929   $54.79   $54.80   $54.80  
  Purchase #4 $238.50   6.137%   $253.1367   $253.14   $253.15   $253.10  
  Purchase #5 $65.40   8.487%   $70.9505   $70.95   $70.95   $71.00  
  Purchase #6 $142.49   10.278%   $157.1351   $157.14   $157.15   $157.10  
  Purchase #7 $117.65   4.461%   $122.8984   $122.90   $122.90   $122.90  
  7 purchase totals = $807.76       $866.9651   $866.97   $867.00   $867.00