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	$238.43	8.846%	$259.5215	$259.52	$259.50	$259.50
Purchase #2	$250.39	3.214%	$258.4375	$258.44	$258.45	$258.40
Purchase #3	$111.93	6.608%	$119.3263	$119.33	$119.35	$119.30
Purchase #4	$193.85	3.643%	$200.912	$200.91	$200.90	$200.90
Purchase #5	$120.39	10.629%	$133.1863	$133.19	$133.20	$133.20
Purchase #6	$71.70	11.620%	$80.0315	$80.03	$80.05	$80.00
Purchase #7	$110.76	11.353%	$123.3346	$123.33	$123.35	$123.30
7 purchase totals =	$1,097.45		$1,174.7497	$1,174.75	$1,174.80	$1,174.60