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	$249.29	6.746%	$266.1071	$266.11	$266.10	$266.10
Purchase #2	$94.94	8.862%	$103.3536	$103.35	$103.35	$103.40
Purchase #3	$111.30	3.565%	$115.2678	$115.27	$115.25	$115.30
Purchase #4	$82.91	9.149%	$90.4954	$90.50	$90.50	$90.50
Purchase #5	$185.97	5.135%	$195.5196	$195.52	$195.50	$195.50
Purchase #6	$110.73	5.730%	$117.0748	$117.07	$117.05	$117.10
Purchase #7	$38.45	10.353%	$42.4307	$42.43	$42.45	$42.40
7 purchase totals =	$873.59		$930.2490	$930.25	$930.20	$930.30