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 $54.42   13.757%   $61.9066   $61.91   $61.90   $61.90  
  Purchase #2 $157.36   5.140%   $165.4483   $165.45   $165.45   $165.40  
  Purchase #3 $125.66   4.286%   $131.0458   $131.05   $131.05   $131.00  
  Purchase #4 $181.92   9.211%   $198.6767   $198.68   $198.70   $198.70  
  Purchase #5 $88.91   13.656%   $101.0515   $101.05   $101.05   $101.10  
  Purchase #6 $107.41   6.168%   $114.035   $114.04   $114.05   $114.00  
  Purchase #7 $35.33   9.652%   $38.7401   $38.74   $38.75   $38.70  
  7 purchase totals = $751.01       $810.9040   $810.92   $810.95   $810.80