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 $56.37   7.274%   $60.4704   $60.47   $60.45   $60.50  
  Purchase #2 $182.34   6.242%   $193.7217   $193.72   $193.70   $193.70  
  Purchase #3 $164.95   9.818%   $181.1448   $181.14   $181.15   $181.10  
  Purchase #4 $150.31   4.737%   $157.4302   $157.43   $157.45   $157.40  
  Purchase #5 $113.91   7.854%   $122.8565   $122.86   $122.85   $122.90  
  Purchase #6 $44.61   9.421%   $48.8127   $48.81   $48.80   $48.80  
  Purchase #7 $156.54   7.493%   $168.2695   $168.27   $168.25   $168.30  
  7 purchase totals = $869.03       $932.7058   $932.70   $932.65   $932.70