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	$5.42	4.463%	$5.6619	$5.66	$5.65	$5.70
Purchase #2	$187.31	11.208%	$208.3037	$208.30	$208.30	$208.30
Purchase #3	$156.33	12.413%	$175.7352	$175.74	$175.75	$175.70
Purchase #4	$174.41	13.774%	$198.4332	$198.43	$198.45	$198.40
Purchase #5	$187.41	5.721%	$198.1317	$198.13	$198.15	$198.10
Purchase #6	$89.61	12.573%	$100.8767	$100.88	$100.90	$100.90
Purchase #7	$111.69	7.522%	$120.0913	$120.09	$120.10	$120.10
7 purchase totals =	$912.18		$1,007.2337	$1,007.23	$1,007.30	$1,007.20