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	$114.76	7.401%	$123.2534	$123.25	$123.25	$123.30
Purchase #2	$93.83	3.778%	$97.3749	$97.37	$97.35	$97.40
Purchase #3	$119.38	10.213%	$131.5723	$131.57	$131.55	$131.60
Purchase #4	$155.67	11.139%	$173.0101	$173.01	$173.00	$173.00
Purchase #5	$89.47	12.195%	$100.3809	$100.38	$100.40	$100.40
Purchase #6	$84.32	4.573%	$88.176	$88.18	$88.20	$88.20
Purchase #7	$118.74	4.364%	$123.9218	$123.92	$123.90	$123.90
7 purchase totals =	$776.17		$837.6894	$837.68	$837.65	$837.80