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	$85.84	4.469%	$89.6762	$89.68	$89.70	$89.70
Purchase #2	$79.46	13.163%	$89.9193	$89.92	$89.90	$89.90
Purchase #3	$30.95	3.657%	$32.0818	$32.08	$32.10	$32.10
Purchase #4	$173.51	13.142%	$196.3127	$196.31	$196.30	$196.30
Purchase #5	$228.71	3.735%	$237.2523	$237.25	$237.25	$237.30
Purchase #6	$5.97	11.135%	$6.6348	$6.63	$6.65	$6.60
Purchase #7	$55.93	13.487%	$63.4733	$63.47	$63.45	$63.50
7 purchase totals =	$660.37		$715.3504	$715.34	$715.35	$715.40