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	$128.48	12.281%	$144.2586	$144.26	$144.25	$144.30
Purchase #2	$155.75	6.773%	$166.2989	$166.30	$166.30	$166.30
Purchase #3	$135.52	4.143%	$141.1346	$141.13	$141.15	$141.10
Purchase #4	$83.71	10.103%	$92.1672	$92.17	$92.15	$92.20
Purchase #5	$195.85	13.418%	$222.1292	$222.13	$222.15	$222.10
Purchase #6	$17.42	8.520%	$18.9042	$18.90	$18.90	$18.90
Purchase #7	$68.50	6.104%	$72.6812	$72.68	$72.70	$72.70
7 purchase totals =	$785.23		$857.5739	$857.57	$857.60	$857.60