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	$123.32	10.393%	$136.1366	$136.14	$136.15	$136.10
Purchase #2	$151.79	9.803%	$166.67	$166.67	$166.65	$166.70
Purchase #3	$6.38	6.558%	$6.7984	$6.80	$6.80	$6.80
Purchase #4	$155.76	11.551%	$173.7518	$173.75	$173.75	$173.80
Purchase #5	$248.38	4.444%	$259.418	$259.42	$259.40	$259.40
Purchase #6	$39.34	10.201%	$43.3531	$43.35	$43.35	$43.40
Purchase #7	$209.86	3.599%	$217.4129	$217.41	$217.40	$217.40
7 purchase totals =	$934.83		$1,003.5408	$1,003.54	$1,003.50	$1,003.60