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	$144.97	10.661%	$160.4253	$160.43	$160.45	$160.40
Purchase #2	$182.48	4.164%	$190.0785	$190.08	$190.10	$190.10
Purchase #3	$230.37	8.232%	$249.3341	$249.33	$249.35	$249.30
Purchase #4	$197.77	5.729%	$209.1002	$209.10	$209.10	$209.10
Purchase #5	$155.57	10.868%	$172.4773	$172.48	$172.50	$172.50
Purchase #6	$56.85	4.218%	$59.2479	$59.25	$59.25	$59.20
Purchase #7	$240.71	10.652%	$266.3504	$266.35	$266.35	$266.40
7 purchase totals =	$1,208.72		$1,307.0137	$1,307.02	$1,307.10	$1,307.00