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	$150.51	10.663%	$166.5589	$166.56	$166.55	$166.60
Purchase #2	$52.72	6.751%	$56.2791	$56.28	$56.30	$56.30
Purchase #3	$108.25	9.457%	$118.4872	$118.49	$118.50	$118.50
Purchase #4	$52.99	3.747%	$54.9755	$54.98	$55.00	$55.00
Purchase #5	$237.73	3.506%	$246.0648	$246.06	$246.05	$246.10
Purchase #6	$242.78	3.600%	$251.5201	$251.52	$251.50	$251.50
Purchase #7	$183.89	3.501%	$190.328	$190.33	$190.35	$190.30
7 purchase totals =	$1,028.87		$1,084.2136	$1,084.22	$1,084.25	$1,084.30