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	$217.32	10.483%	$240.1017	$240.10	$240.10	$240.10
Purchase #2	$94.47	9.562%	$103.5032	$103.50	$103.50	$103.50
Purchase #3	$180.31	8.425%	$195.5011	$195.50	$195.50	$195.50
Purchase #4	$178.50	11.186%	$198.467	$198.47	$198.45	$198.50
Purchase #5	$53.90	13.184%	$61.0062	$61.01	$61.00	$61.00
Purchase #6	$18.79	3.338%	$19.4172	$19.42	$19.40	$19.40
Purchase #7	$105.41	7.107%	$112.9015	$112.90	$112.90	$112.90
7 purchase totals =	$848.70		$930.8979	$930.90	$930.85	$930.90