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	$158.61	13.478%	$179.9875	$179.99	$180.00	$180.00
Purchase #2	$98.99	12.212%	$111.0787	$111.08	$111.10	$111.10
Purchase #3	$188.29	9.346%	$205.8876	$205.89	$205.90	$205.90
Purchase #4	$195.29	10.527%	$215.8482	$215.85	$215.85	$215.80
Purchase #5	$48.29	5.621%	$51.0044	$51.00	$51.00	$51.00
Purchase #6	$171.53	8.367%	$185.8819	$185.88	$185.90	$185.90
Purchase #7	$130.30	7.399%	$139.9409	$139.94	$139.95	$139.90
7 purchase totals =	$991.30		$1,089.6292	$1,089.63	$1,089.70	$1,089.60