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 $207.79   8.263%   $224.9597   $224.96   $224.95   $225.00  
  Purchase #2 $134.49   10.757%   $148.9571   $148.96   $148.95   $149.00  
  Purchase #3 $162.35   3.233%   $167.5988   $167.60   $167.60   $167.60  
  Purchase #4 $82.84   9.491%   $90.7023   $90.70   $90.70   $90.70  
  Purchase #5 $154.90   10.635%   $171.3736   $171.37   $171.35   $171.40  
  Purchase #6 $112.65   8.182%   $121.867   $121.87   $121.85   $121.90  
  Purchase #7 $74.47   6.774%   $79.5146   $79.51   $79.50   $79.50  
  7 purchase totals = $929.49       $1,004.9731   $1,004.97   $1,004.90   $1,005.10