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	$158.58	5.557%	$167.3923	$167.39	$167.40	$167.40
Purchase #2	$111.92	9.649%	$122.7192	$122.72	$122.70	$122.70
Purchase #3	$90.97	10.783%	$100.7793	$100.78	$100.80	$100.80
Purchase #4	$225.35	4.567%	$235.6417	$235.64	$235.65	$235.60
Purchase #5	$107.30	3.681%	$111.2497	$111.25	$111.25	$111.20
Purchase #6	$89.54	11.196%	$99.5649	$99.56	$99.55	$99.60
Purchase #7	$229.72	13.486%	$260.7	$260.70	$260.70	$260.70
7 purchase totals =	$1,013.38		$1,098.0471	$1,098.04	$1,098.05	$1,098.00