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 $67.32   5.773%   $71.2064   $71.21   $71.20   $71.20  
  Purchase #2 $147.89   4.469%   $154.4992   $154.50   $154.50   $154.50  
  Purchase #3 $63.86   4.685%   $66.8518   $66.85   $66.85   $66.90  
  Purchase #4 $233.78   5.177%   $245.8828   $245.88   $245.90   $245.90  
  Purchase #5 $207.96   11.362%   $231.5884   $231.59   $231.60   $231.60  
  Purchase #6 $192.26   11.633%   $214.6256   $214.63   $214.65   $214.60  
  Purchase #7 $75.66   5.240%   $79.6246   $79.62   $79.60   $79.60  
  7 purchase totals = $988.73       $1,064.2788   $1,064.28   $1,064.30   $1,064.30