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 $91.86   5.497%   $96.9095   $96.91   $96.90   $96.90  
  Purchase #2 $224.47   7.217%   $240.67   $240.67   $240.65   $240.70  
  Purchase #3 $173.40   4.634%   $181.4354   $181.44   $181.45   $181.40  
  Purchase #4 $178.32   5.557%   $188.2292   $188.23   $188.25   $188.20  
  Purchase #5 $99.47   6.639%   $106.0738   $106.07   $106.05   $106.10  
  Purchase #6 $242.32   3.209%   $250.096   $250.10   $250.10   $250.10  
  Purchase #7 $197.29   5.670%   $208.4763   $208.48   $208.50   $208.50  
  7 purchase totals = $1,207.13       $1,271.8902   $1,271.90   $1,271.90   $1,271.90