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 $110.40   4.323%   $115.1726   $115.17   $115.15   $115.20  
  Purchase #2 $237.78   8.461%   $257.8986   $257.90   $257.90   $257.90  
  Purchase #3 $196.46   4.696%   $205.6858   $205.69   $205.70   $205.70  
  Purchase #4 $169.27   4.481%   $176.855   $176.86   $176.85   $176.90  
  Purchase #5 $241.68   10.132%   $266.167   $266.17   $266.15   $266.20  
  Purchase #6 $221.71   5.647%   $234.23   $234.23   $234.25   $234.20  
  Purchase #7 $150.25   4.138%   $156.4673   $156.47   $156.45   $156.50  
  7 purchase totals = $1,327.55       $1,412.4763   $1,412.49   $1,412.45   $1,412.60