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	$122.92	3.463%	$127.1767	$127.18	$127.20	$127.20
Purchase #2	$64.76	7.844%	$69.8398	$69.84	$69.85	$69.80
Purchase #3	$35.42	5.478%	$37.3603	$37.36	$37.35	$37.40
Purchase #4	$52.44	9.308%	$57.3211	$57.32	$57.30	$57.30
Purchase #5	$124.93	10.302%	$137.8003	$137.80	$137.80	$137.80
Purchase #6	$116.83	5.369%	$123.1026	$123.10	$123.10	$123.10
Purchase #7	$105.95	10.498%	$117.0726	$117.07	$117.05	$117.10
7 purchase totals =	$623.25		$669.6734	$669.67	$669.65	$669.70