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	$78.37	10.717%	$86.7689	$86.77	$86.75	$86.80
Purchase #2	$126.73	6.489%	$134.9535	$134.95	$134.95	$135.00
Purchase #3	$82.56	3.625%	$85.5528	$85.55	$85.55	$85.60
Purchase #4	$126.46	7.233%	$135.6069	$135.61	$135.60	$135.60
Purchase #5	$89.52	11.806%	$100.0887	$100.09	$100.10	$100.10
Purchase #6	$164.28	12.162%	$184.2597	$184.26	$184.25	$184.30
Purchase #7	$131.99	5.705%	$139.52	$139.52	$139.50	$139.50
7 purchase totals =	$799.91		$866.7505	$866.75	$866.70	$866.90