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	$230.26	11.196%	$256.0399	$256.04	$256.05	$256.00
Purchase #2	$155.34	5.760%	$164.2876	$164.29	$164.30	$164.30
Purchase #3	$49.98	9.296%	$54.6261	$54.63	$54.65	$54.60
Purchase #4	$53.27	11.234%	$59.2544	$59.25	$59.25	$59.30
Purchase #5	$236.48	7.832%	$255.0011	$255.00	$255.00	$255.00
Purchase #6	$176.94	12.365%	$198.8186	$198.82	$198.80	$198.80
Purchase #7	$7.58	8.429%	$8.2189	$8.22	$8.20	$8.20
7 purchase totals =	$909.85		$996.2466	$996.25	$996.25	$996.20