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	$14.71	8.783%	$16.002	$16.00	$16.00	$16.00
Purchase #2	$142.93	12.260%	$160.4532	$160.45	$160.45	$160.50
Purchase #3	$50.60	5.288%	$53.2757	$53.28	$53.30	$53.30
Purchase #4	$247.91	11.223%	$275.7329	$275.73	$275.75	$275.70
Purchase #5	$220.35	6.843%	$235.4286	$235.43	$235.45	$235.40
Purchase #6	$89.77	11.494%	$100.0882	$100.09	$100.10	$100.10
Purchase #7	$183.98	6.790%	$196.4722	$196.47	$196.45	$196.50
7 purchase totals =	$950.25		$1,037.4528	$1,037.45	$1,037.50	$1,037.50