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	$70.98	11.553%	$79.1803	$79.18	$79.20	$79.20
Purchase #2	$127.63	9.479%	$139.728	$139.73	$139.75	$139.70
Purchase #3	$5.77	8.708%	$6.2725	$6.27	$6.25	$6.30
Purchase #4	$38.66	10.126%	$42.5747	$42.57	$42.55	$42.60
Purchase #5	$42.41	12.502%	$47.7121	$47.71	$47.70	$47.70
Purchase #6	$88.46	12.722%	$99.7139	$99.71	$99.70	$99.70
Purchase #7	$215.46	8.183%	$233.0911	$233.09	$233.10	$233.10
7 purchase totals =	$589.37		$648.2726	$648.26	$648.25	$648.30