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	$175.59	12.153%	$196.9295	$196.93	$196.95	$196.90
Purchase #2	$105.27	3.336%	$108.7818	$108.78	$108.80	$108.80
Purchase #3	$175.70	11.859%	$196.5363	$196.54	$196.55	$196.50
Purchase #4	$29.77	7.117%	$31.8887	$31.89	$31.90	$31.90
Purchase #5	$39.28	10.743%	$43.4999	$43.50	$43.50	$43.50
Purchase #6	$42.51	8.409%	$46.0847	$46.08	$46.10	$46.10
Purchase #7	$49.88	11.735%	$55.7334	$55.73	$55.75	$55.70
7 purchase totals =	$618.00		$679.4543	$679.45	$679.55	$679.40