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	$53.62	8.718%	$58.2946	$58.29	$58.30	$58.30
Purchase #2	$111.83	9.243%	$122.1664	$122.17	$122.15	$122.20
Purchase #3	$173.90	3.121%	$179.3274	$179.33	$179.35	$179.30
Purchase #4	$33.25	4.680%	$34.8061	$34.81	$34.80	$34.80
Purchase #5	$104.34	8.595%	$113.308	$113.31	$113.30	$113.30
Purchase #6	$111.54	3.222%	$115.1338	$115.13	$115.15	$115.10
Purchase #7	$40.64	10.271%	$44.8141	$44.81	$44.80	$44.80
7 purchase totals =	$629.12		$667.8504	$667.85	$667.85	$667.80