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	$200.30	9.290%	$218.9079	$218.91	$218.90	$218.90
Purchase #2	$89.62	13.683%	$101.8827	$101.88	$101.90	$101.90
Purchase #3	$103.67	10.828%	$114.8954	$114.90	$114.90	$114.90
Purchase #4	$232.87	13.597%	$264.5333	$264.53	$264.55	$264.50
Purchase #5	$95.60	8.762%	$103.9765	$103.98	$104.00	$104.00
Purchase #6	$249.46	6.800%	$266.4233	$266.42	$266.40	$266.40
Purchase #7	$27.77	3.126%	$28.6381	$28.64	$28.65	$28.60
7 purchase totals =	$999.29		$1,099.2572	$1,099.26	$1,099.30	$1,099.20