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	$82.75	8.408%	$89.7076	$89.71	$89.70	$89.70
Purchase #2	$216.39	10.253%	$238.5765	$238.58	$238.60	$238.60
Purchase #3	$241.37	4.337%	$251.8382	$251.84	$251.85	$251.80
Purchase #4	$12.94	9.265%	$14.1389	$14.14	$14.15	$14.10
Purchase #5	$184.51	13.225%	$208.9114	$208.91	$208.90	$208.90
Purchase #6	$67.84	13.205%	$76.7983	$76.80	$76.80	$76.80
Purchase #7	$125.50	11.216%	$139.5761	$139.58	$139.60	$139.60
7 purchase totals =	$931.30		$1,019.5470	$1,019.56	$1,019.60	$1,019.50