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	$30.49	4.646%	$31.9066	$31.91	$31.90	$31.90
Purchase #2	$163.62	6.502%	$174.2586	$174.26	$174.25	$174.30
Purchase #3	$179.77	10.198%	$198.1029	$198.10	$198.10	$198.10
Purchase #4	$99.85	11.575%	$111.4076	$111.41	$111.40	$111.40
Purchase #5	$188.25	5.135%	$197.9166	$197.92	$197.90	$197.90
Purchase #6	$103.31	11.192%	$114.8725	$114.87	$114.85	$114.90
Purchase #7	$177.42	6.429%	$188.8263	$188.83	$188.85	$188.80
7 purchase totals =	$942.71		$1,017.2911	$1,017.30	$1,017.25	$1,017.30