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 $225.70   11.653%   $252.0008   $252.00   $252.00   $252.00  
  Purchase #2 $118.33   13.532%   $134.3424   $134.34   $134.35   $134.30  
  Purchase #3 $58.64   4.131%   $61.0624   $61.06   $61.05   $61.10  
  Purchase #4 $44.94   6.471%   $47.8481   $47.85   $47.85   $47.80  
  Purchase #5 $127.45   9.452%   $139.4966   $139.50   $139.50   $139.50  
  Purchase #6 $164.35   6.678%   $175.3253   $175.33   $175.35   $175.30  
  Purchase #7 $113.64   11.748%   $126.9904   $126.99   $127.00   $127.00  
  7 purchase totals = $853.05       $937.0660   $937.07   $937.10   $937.00