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 $56.66   8.366%   $61.4002   $61.40   $61.40   $61.40  
  Purchase #2 $175.62   7.819%   $189.3517   $189.35   $189.35   $189.40  
  Purchase #3 $101.65   5.535%   $107.2763   $107.28   $107.30   $107.30  
  Purchase #4 $16.39   4.277%   $17.091   $17.09   $17.10   $17.10  
  Purchase #5 $209.68   12.303%   $235.4769   $235.48   $235.50   $235.50  
  Purchase #6 $234.68   5.681%   $248.0122   $248.01   $248.00   $248.00  
  Purchase #7 $89.27   8.552%   $96.9044   $96.90   $96.90   $96.90  
  7 purchase totals = $883.95       $955.5127   $955.51   $955.55   $955.60