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	$81.54	10.244%	$89.893	$89.89	$89.90	$89.90
Purchase #2	$242.52	11.739%	$270.9894	$270.99	$271.00	$271.00
Purchase #3	$204.31	3.588%	$211.6406	$211.64	$211.65	$211.60
Purchase #4	$51.84	4.750%	$54.3024	$54.30	$54.30	$54.30
Purchase #5	$236.33	12.256%	$265.2946	$265.29	$265.30	$265.30
Purchase #6	$133.27	10.549%	$147.3287	$147.33	$147.35	$147.30
Purchase #7	$31.47	12.586%	$35.4308	$35.43	$35.45	$35.40
7 purchase totals =	$981.28		$1,074.8795	$1,074.87	$1,074.95	$1,074.80