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 $114.79   9.105%   $125.2416   $125.24   $125.25   $125.20  
  Purchase #2 $178.68   6.240%   $189.8296   $189.83   $189.85   $189.80  
  Purchase #3 $229.93   7.825%   $247.922   $247.92   $247.90   $247.90  
  Purchase #4 $233.36   4.577%   $244.0409   $244.04   $244.05   $244.00  
  Purchase #5 $165.56   9.812%   $181.8047   $181.80   $181.80   $181.80  
  Purchase #6 $142.69   11.670%   $159.3419   $159.34   $159.35   $159.30  
  Purchase #7 $65.25   6.836%   $69.7105   $69.71   $69.70   $69.70  
  7 purchase totals = $1,130.26       $1,217.8912   $1,217.88   $1,217.90   $1,217.70