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	$84.32	6.477%	$89.7814	$89.78	$89.80	$89.80
Purchase #2	$163.72	4.764%	$171.5196	$171.52	$171.50	$171.50
Purchase #3	$164.27	8.518%	$178.2625	$178.26	$178.25	$178.30
Purchase #4	$147.87	4.398%	$154.3733	$154.37	$154.35	$154.40
Purchase #5	$45.74	5.104%	$48.0746	$48.07	$48.05	$48.10
Purchase #6	$226.25	5.147%	$237.8951	$237.90	$237.90	$237.90
Purchase #7	$221.76	4.294%	$231.2824	$231.28	$231.30	$231.30
7 purchase totals =	$1,053.93		$1,111.1889	$1,111.18	$1,111.15	$1,111.30