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	$67.74	7.560%	$72.8611	$72.86	$72.85	$72.90
Purchase #2	$137.52	10.408%	$151.8331	$151.83	$151.85	$151.80
Purchase #3	$111.84	12.762%	$126.113	$126.11	$126.10	$126.10
Purchase #4	$120.91	8.651%	$131.3699	$131.37	$131.35	$131.40
Purchase #5	$91.87	9.853%	$100.922	$100.92	$100.90	$100.90
Purchase #6	$208.90	11.329%	$232.5663	$232.57	$232.55	$232.60
Purchase #7	$23.98	7.563%	$25.7936	$25.79	$25.80	$25.80
7 purchase totals =	$762.76		$841.4590	$841.45	$841.40	$841.50