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 $230.76   13.743%   $262.4733   $262.47   $262.45   $262.50  
  Purchase #2 $15.36   9.800%   $16.8653   $16.87   $16.85   $16.90  
  Purchase #3 $183.54   12.162%   $205.8621   $205.86   $205.85   $205.90  
  Purchase #4 $55.76   10.485%   $61.6064   $61.61   $61.60   $61.60  
  Purchase #5 $195.76   8.303%   $212.014   $212.01   $212.00   $212.00  
  Purchase #6 $157.27   4.791%   $164.8048   $164.80   $164.80   $164.80  
  Purchase #7 $231.35   8.703%   $251.4844   $251.48   $251.50   $251.50  
  7 purchase totals = $1,069.80       $1,175.1103   $1,175.10   $1,175.05   $1,175.20