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	$225.33	13.734%	$256.2768	$256.28	$256.30	$256.30
Purchase #2	$65.94	4.838%	$69.1302	$69.13	$69.15	$69.10
Purchase #3	$35.55	6.272%	$37.7797	$37.78	$37.80	$37.80
Purchase #4	$198.43	9.653%	$217.5844	$217.58	$217.60	$217.60
Purchase #5	$159.41	4.704%	$166.9086	$166.91	$166.90	$166.90
Purchase #6	$91.54	5.811%	$96.8594	$96.86	$96.85	$96.90
Purchase #7	$221.93	9.250%	$242.4585	$242.46	$242.45	$242.50
7 purchase totals =	$998.13		$1,086.9976	$1,087.00	$1,087.05	$1,087.10