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	$40.54	8.335%	$43.919	$43.92	$43.90	$43.90
Purchase #2	$159.32	7.238%	$170.8516	$170.85	$170.85	$170.90
Purchase #3	$205.78	10.425%	$227.2326	$227.23	$227.25	$227.20
Purchase #4	$47.83	11.855%	$53.5002	$53.50	$53.50	$53.50
Purchase #5	$187.69	12.115%	$210.4286	$210.43	$210.45	$210.40
Purchase #6	$71.59	11.760%	$80.009	$80.01	$80.00	$80.00
Purchase #7	$92.62	4.488%	$96.7768	$96.78	$96.80	$96.80
7 purchase totals =	$805.37		$882.7178	$882.72	$882.75	$882.70