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	$72.53	10.576%	$80.2008	$80.20	$80.20	$80.20
Purchase #2	$194.67	8.215%	$210.6621	$210.66	$210.65	$210.70
Purchase #3	$51.86	9.831%	$56.9584	$56.96	$56.95	$57.00
Purchase #4	$132.86	13.754%	$151.1336	$151.13	$151.15	$151.10
Purchase #5	$173.29	13.199%	$196.1625	$196.16	$196.15	$196.20
Purchase #6	$183.91	4.516%	$192.2154	$192.22	$192.20	$192.20
Purchase #7	$187.52	12.162%	$210.3262	$210.33	$210.35	$210.30
7 purchase totals =	$996.64		$1,097.6590	$1,097.66	$1,097.65	$1,097.70