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 $86.89   7.655%   $93.5414   $93.54   $93.55   $93.50  
  Purchase #2 $222.82   12.604%   $250.9042   $250.90   $250.90   $250.90  
  Purchase #3 $114.49   6.532%   $121.9685   $121.97   $121.95   $122.00  
  Purchase #4 $188.99   3.320%   $195.2645   $195.26   $195.25   $195.30  
  Purchase #5 $235.31   7.642%   $253.2924   $253.29   $253.30   $253.30  
  Purchase #6 $208.34   4.374%   $217.4528   $217.45   $217.45   $217.50  
  Purchase #7 $109.94   7.424%   $118.1019   $118.10   $118.10   $118.10  
  7 purchase totals = $1,166.78       $1,250.5257   $1,250.51   $1,250.50   $1,250.60