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 $240.85   5.433%   $253.9354   $253.94   $253.95   $253.90  
  Purchase #2 $235.36   5.400%   $248.0694   $248.07   $248.05   $248.10  
  Purchase #3 $249.51   6.456%   $265.6184   $265.62   $265.60   $265.60  
  Purchase #4 $222.58   11.393%   $247.9385   $247.94   $247.95   $247.90  
  Purchase #5 $41.93   7.378%   $45.0236   $45.02   $45.00   $45.00  
  Purchase #6 $215.45   7.738%   $232.1215   $232.12   $232.10   $232.10  
  Purchase #7 $57.25   9.295%   $62.5714   $62.57   $62.55   $62.60  
  7 purchase totals = $1,262.93       $1,355.2782   $1,355.28   $1,355.20   $1,355.20