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 $241.67   9.797%   $265.3464   $265.35   $265.35   $265.30  
  Purchase #2 $181.69   7.528%   $195.3676   $195.37   $195.35   $195.40  
  Purchase #3 $72.79   5.589%   $76.8582   $76.86   $76.85   $76.90  
  Purchase #4 $244.30   11.865%   $273.2862   $273.29   $273.30   $273.30  
  Purchase #5 $27.87   10.148%   $30.6982   $30.70   $30.70   $30.70  
  Purchase #6 $128.64   8.283%   $139.2953   $139.30   $139.30   $139.30  
  Purchase #7 $23.51   9.477%   $25.738   $25.74   $25.75   $25.70  
  7 purchase totals = $920.47       $1,006.5899   $1,006.61   $1,006.60   $1,006.60