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	$229.84	11.160%	$255.4901	$255.49	$255.50	$255.50
Purchase #2	$95.71	9.601%	$104.8991	$104.90	$104.90	$104.90
Purchase #3	$221.43	5.490%	$233.5865	$233.59	$233.60	$233.60
Purchase #4	$96.55	3.274%	$99.711	$99.71	$99.70	$99.70
Purchase #5	$36.26	8.758%	$39.4357	$39.44	$39.45	$39.40
Purchase #6	$158.67	8.531%	$172.2061	$172.21	$172.20	$172.20
Purchase #7	$151.86	10.280%	$167.4712	$167.47	$167.45	$167.50
7 purchase totals =	$990.32		$1,072.7997	$1,072.81	$1,072.80	$1,072.80