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	$15.39	11.489%	$17.1582	$17.16	$17.15	$17.20
Purchase #2	$11.59	13.477%	$13.152	$13.15	$13.15	$13.20
Purchase #3	$166.90	11.106%	$185.4359	$185.44	$185.45	$185.40
Purchase #4	$105.36	8.566%	$114.3851	$114.39	$114.40	$114.40
Purchase #5	$175.26	13.222%	$198.4329	$198.43	$198.45	$198.40
Purchase #6	$32.45	12.809%	$36.6065	$36.61	$36.60	$36.60
Purchase #7	$79.38	11.632%	$88.6135	$88.61	$88.60	$88.60
7 purchase totals =	$586.33		$653.7841	$653.79	$653.80	$653.80