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	$78.78	4.590%	$82.396	$82.40	$82.40	$82.40
Purchase #2	$52.77	9.675%	$57.8755	$57.88	$57.90	$57.90
Purchase #3	$108.49	5.692%	$114.6653	$114.67	$114.65	$114.70
Purchase #4	$93.47	5.148%	$98.2818	$98.28	$98.30	$98.30
Purchase #5	$215.38	8.285%	$233.2242	$233.22	$233.20	$233.20
Purchase #6	$42.82	13.271%	$48.5026	$48.50	$48.50	$48.50
Purchase #7	$159.56	13.402%	$180.9442	$180.94	$180.95	$180.90
7 purchase totals =	$751.27		$815.8896	$815.89	$815.90	$815.90