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 $241.45   8.742%   $262.5576   $262.56   $262.55   $262.60  
  Purchase #2 $150.78   9.670%   $165.3604   $165.36   $165.35   $165.40  
  Purchase #3 $175.71   6.739%   $187.5511   $187.55   $187.55   $187.60  
  Purchase #4 $249.66   3.138%   $257.4943   $257.49   $257.50   $257.50  
  Purchase #5 $198.56   8.362%   $215.1636   $215.16   $215.15   $215.20  
  Purchase #6 $124.78   13.739%   $141.9235   $141.92   $141.90   $141.90  
  Purchase #7 $51.77   8.523%   $56.1824   $56.18   $56.20   $56.20  
  7 purchase totals = $1,192.71       $1,286.2329   $1,286.22   $1,286.20   $1,286.40