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	$139.78	7.384%	$150.1014	$150.10	$150.10	$150.10
Purchase #2	$139.49	3.598%	$144.5089	$144.51	$144.50	$144.50
Purchase #3	$167.84	11.478%	$187.1047	$187.10	$187.10	$187.10
Purchase #4	$46.52	9.761%	$51.0608	$51.06	$51.05	$51.10
Purchase #5	$235.57	9.254%	$257.3696	$257.37	$257.35	$257.40
Purchase #6	$184.78	3.222%	$190.7336	$190.73	$190.75	$190.70
Purchase #7	$57.42	8.731%	$62.4333	$62.43	$62.45	$62.40
7 purchase totals =	$971.40		$1,043.3123	$1,043.30	$1,043.30	$1,043.30