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	$249.65	3.480%	$258.3378	$258.34	$258.35	$258.30
Purchase #2	$52.99	11.622%	$59.1485	$59.15	$59.15	$59.10
Purchase #3	$106.31	6.844%	$113.5859	$113.59	$113.60	$113.60
Purchase #4	$223.70	4.195%	$233.0842	$233.08	$233.10	$233.10
Purchase #5	$191.78	4.685%	$200.7649	$200.76	$200.75	$200.80
Purchase #6	$244.55	9.373%	$267.4717	$267.47	$267.45	$267.50
Purchase #7	$122.71	6.435%	$130.6064	$130.61	$130.60	$130.60
7 purchase totals =	$1,191.69		$1,262.9994	$1,263.00	$1,263.00	$1,263.00