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 $142.34   6.470%   $151.5494   $151.55   $151.55   $151.50  
  Purchase #2 $49.54   4.682%   $51.8595   $51.86   $51.85   $51.90  
  Purchase #3 $187.26   8.477%   $203.134   $203.13   $203.15   $203.10  
  Purchase #4 $214.93   11.548%   $239.7501   $239.75   $239.75   $239.80  
  Purchase #5 $10.49   13.692%   $11.9263   $11.93   $11.95   $11.90  
  Purchase #6 $231.80   7.371%   $248.886   $248.89   $248.90   $248.90  
  Purchase #7 $191.85   5.740%   $202.8622   $202.86   $202.85   $202.90  
  7 purchase totals = $1,028.21       $1,109.9675   $1,109.97   $1,110.00   $1,110.00