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 $31.88   8.575%   $34.6137   $34.61   $34.60   $34.60  
  Purchase #2 $247.37   5.687%   $261.4379   $261.44   $261.45   $261.40  
  Purchase #3 $222.64   12.248%   $249.9089   $249.91   $249.90   $249.90  
  Purchase #4 $181.83   5.399%   $191.647   $191.65   $191.65   $191.60  
  Purchase #5 $167.27   13.737%   $190.2479   $190.25   $190.25   $190.20  
  Purchase #6 $16.69   13.521%   $18.9467   $18.95   $18.95   $18.90  
  Purchase #7 $134.37   9.513%   $147.1526   $147.15   $147.15   $147.20  
  7 purchase totals = $1,002.05       $1,093.9547   $1,093.96   $1,093.95   $1,093.80