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	$241.67	10.244%	$266.4267	$266.43	$266.45	$266.40
Purchase #2	$39.55	8.108%	$42.7567	$42.76	$42.75	$42.80
Purchase #3	$122.48	11.765%	$136.8898	$136.89	$136.90	$136.90
Purchase #4	$52.56	6.788%	$56.1278	$56.13	$56.15	$56.10
Purchase #5	$25.78	8.799%	$28.0484	$28.05	$28.05	$28.00
Purchase #6	$200.94	7.297%	$215.6026	$215.60	$215.60	$215.60
Purchase #7	$79.95	12.400%	$89.8638	$89.86	$89.85	$89.90
7 purchase totals =	$762.93		$835.7158	$835.72	$835.75	$835.70