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 $151.38   5.542%   $159.7695   $159.77   $159.75   $159.80  
  Purchase #2 $79.95   9.380%   $87.4493   $87.45   $87.45   $87.40  
  Purchase #3 $168.54   7.675%   $181.4754   $181.48   $181.50   $181.50  
  Purchase #4 $56.71   6.274%   $60.268   $60.27   $60.25   $60.30  
  Purchase #5 $171.92   9.270%   $187.857   $187.86   $187.85   $187.90  
  Purchase #6 $166.59   5.648%   $175.999   $176.00   $176.00   $176.00  
  Purchase #7 $198.50   4.785%   $207.9982   $208.00   $208.00   $208.00  
  7 purchase totals = $993.59       $1,060.8164   $1,060.83   $1,060.80   $1,060.90