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	$39.87	3.445%	$41.2435	$41.24	$41.25	$41.20
Purchase #2	$233.95	9.570%	$256.339	$256.34	$256.35	$256.30
Purchase #3	$56.35	5.614%	$59.5135	$59.51	$59.50	$59.50
Purchase #4	$71.27	3.291%	$73.6155	$73.62	$73.60	$73.60
Purchase #5	$35.91	12.873%	$40.5327	$40.53	$40.55	$40.50
Purchase #6	$234.68	11.792%	$262.3535	$262.35	$262.35	$262.40
Purchase #7	$178.45	4.867%	$187.1352	$187.14	$187.15	$187.10
7 purchase totals =	$850.48		$920.7329	$920.73	$920.75	$920.60