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 $70.40   6.873%   $75.2386   $75.24   $75.25   $75.20  
  Purchase #2 $134.43   4.814%   $140.9015   $140.90   $140.90   $140.90  
  Purchase #3 $70.77   7.122%   $75.8102   $75.81   $75.80   $75.80  
  Purchase #4 $215.31   8.778%   $234.2099   $234.21   $234.20   $234.20  
  Purchase #5 $123.64   5.529%   $130.4761   $130.48   $130.50   $130.50  
  Purchase #6 $56.66   6.357%   $60.2619   $60.26   $60.25   $60.30  
  Purchase #7 $232.51   8.490%   $252.2501   $252.25   $252.25   $252.30  
  7 purchase totals = $903.72       $969.1483   $969.15   $969.15   $969.20