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 $193.90   10.327%   $213.9241   $213.92   $213.90   $213.90  
  Purchase #2 $119.81   12.228%   $134.4604   $134.46   $134.45   $134.50  
  Purchase #3 $78.67   6.414%   $83.7159   $83.72   $83.70   $83.70  
  Purchase #4 $120.81   4.618%   $126.389   $126.39   $126.40   $126.40  
  Purchase #5 $234.81   10.643%   $259.8008   $259.80   $259.80   $259.80  
  Purchase #6 $236.48   9.801%   $259.6574   $259.66   $259.65   $259.70  
  Purchase #7 $201.43   9.761%   $221.0916   $221.09   $221.10   $221.10  
  7 purchase totals = $1,185.91       $1,299.0392   $1,299.04   $1,299.00   $1,299.10