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	$41.55	3.636%	$43.0608	$43.06	$43.05	$43.10
Purchase #2	$80.49	4.606%	$84.1974	$84.20	$84.20	$84.20
Purchase #3	$129.61	12.271%	$145.5144	$145.51	$145.50	$145.50
Purchase #4	$107.66	3.589%	$111.5239	$111.52	$111.50	$111.50
Purchase #5	$118.62	7.323%	$127.3065	$127.31	$127.30	$127.30
Purchase #6	$73.84	5.803%	$78.1249	$78.12	$78.10	$78.10
Purchase #7	$8.39	4.457%	$8.7639	$8.76	$8.75	$8.80
7 purchase totals =	$560.16		$598.4918	$598.48	$598.40	$598.50