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 $53.89   11.320%   $59.9903   $59.99   $60.00   $60.00  
  Purchase #2 $114.37   3.122%   $117.9406   $117.94   $117.95   $117.90  
  Purchase #3 $180.40   7.163%   $193.3221   $193.32   $193.30   $193.30  
  Purchase #4 $139.88   8.164%   $151.2998   $151.30   $151.30   $151.30  
  Purchase #5 $175.69   6.575%   $187.2416   $187.24   $187.25   $187.20  
  Purchase #6 $41.62   6.576%   $44.3569   $44.36   $44.35   $44.40  
  Purchase #7 $250.90   7.696%   $270.2093   $270.21   $270.20   $270.20  
  7 purchase totals = $956.75       $1,024.3606   $1,024.36   $1,024.35   $1,024.30