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 $188.64   11.154%   $209.6809   $209.68   $209.70   $209.70  
  Purchase #2 $55.95   10.108%   $61.6054   $61.61   $61.60   $61.60  
  Purchase #3 $86.71   6.807%   $92.6123   $92.61   $92.60   $92.60  
  Purchase #4 $117.49   6.812%   $125.4934   $125.49   $125.50   $125.50  
  Purchase #5 $100.94   6.637%   $107.6394   $107.64   $107.65   $107.60  
  Purchase #6 $30.73   4.432%   $32.092   $32.09   $32.10   $32.10  
  Purchase #7 $241.40   3.142%   $248.9848   $248.98   $249.00   $249.00  
  7 purchase totals = $821.86       $878.1082   $878.10   $878.15   $878.10