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 $40.68   13.109%   $46.0127   $46.01   $46.00   $46.00  
  Purchase #2 $146.93   6.276%   $156.1513   $156.15   $156.15   $156.20  
  Purchase #3 $149.39   10.204%   $164.6338   $164.63   $164.65   $164.60  
  Purchase #4 $130.99   13.510%   $148.6867   $148.69   $148.70   $148.70  
  Purchase #5 $145.26   9.616%   $159.2282   $159.23   $159.25   $159.20  
  Purchase #6 $222.45   13.836%   $253.2282   $253.23   $253.25   $253.20  
  Purchase #7 $90.27   6.790%   $96.3993   $96.40   $96.40   $96.40  
  7 purchase totals = $925.97       $1,024.3402   $1,024.34   $1,024.40   $1,024.30