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	$142.86	13.507%	$162.1561	$162.16	$162.15	$162.20
Purchase #2	$121.34	8.189%	$131.2765	$131.28	$131.30	$131.30
Purchase #3	$155.37	12.441%	$174.6996	$174.70	$174.70	$174.70
Purchase #4	$81.35	10.539%	$89.9235	$89.92	$89.90	$89.90
Purchase #5	$166.34	11.649%	$185.7169	$185.72	$185.70	$185.70
Purchase #6	$61.97	10.388%	$68.4074	$68.41	$68.40	$68.40
Purchase #7	$239.41	11.151%	$266.1066	$266.11	$266.10	$266.10
7 purchase totals =	$968.64		$1,078.2866	$1,078.30	$1,078.25	$1,078.30