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	$180.82	9.772%	$198.4897	$198.49	$198.50	$198.50
Purchase #2	$107.67	3.836%	$111.8002	$111.80	$111.80	$111.80
Purchase #3	$202.26	9.307%	$221.0843	$221.08	$221.10	$221.10
Purchase #4	$82.44	7.324%	$88.4779	$88.48	$88.50	$88.50
Purchase #5	$226.33	10.345%	$249.7438	$249.74	$249.75	$249.70
Purchase #6	$177.97	5.539%	$187.8278	$187.83	$187.85	$187.80
Purchase #7	$62.29	13.204%	$70.5148	$70.51	$70.50	$70.50
7 purchase totals =	$1,039.78		$1,127.9385	$1,127.93	$1,128.00	$1,127.90