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	$69.62	13.357%	$78.9191	$78.92	$78.90	$78.90
Purchase #2	$217.77	3.313%	$224.9847	$224.98	$225.00	$225.00
Purchase #3	$231.76	3.791%	$240.546	$240.55	$240.55	$240.50
Purchase #4	$132.93	13.607%	$151.0178	$151.02	$151.00	$151.00
Purchase #5	$50.52	13.375%	$57.2771	$57.28	$57.30	$57.30
Purchase #6	$32.93	6.602%	$35.104	$35.10	$35.10	$35.10
Purchase #7	$92.29	10.661%	$102.129	$102.13	$102.15	$102.10
7 purchase totals =	$827.82		$889.9777	$889.98	$890.00	$889.90