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	$80.49	10.702%	$89.104	$89.10	$89.10	$89.10
Purchase #2	$92.44	4.705%	$96.7893	$96.79	$96.80	$96.80
Purchase #3	$212.71	4.404%	$222.0777	$222.08	$222.10	$222.10
Purchase #4	$136.51	6.167%	$144.9286	$144.93	$144.95	$144.90
Purchase #5	$163.85	6.422%	$174.3724	$174.37	$174.35	$174.40
Purchase #6	$213.97	4.247%	$223.0573	$223.06	$223.05	$223.10
Purchase #7	$153.59	11.255%	$170.8766	$170.88	$170.90	$170.90
7 purchase totals =	$1,053.56		$1,121.2059	$1,121.21	$1,121.25	$1,121.30