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	$71.83	13.456%	$81.4954	$81.50	$81.50	$81.50
Purchase #2	$144.53	4.705%	$151.3301	$151.33	$151.35	$151.30
Purchase #3	$136.72	3.590%	$141.6282	$141.63	$141.65	$141.60
Purchase #4	$50.62	6.400%	$53.8597	$53.86	$53.85	$53.90
Purchase #5	$31.26	7.202%	$33.5113	$33.51	$33.50	$33.50
Purchase #6	$166.43	7.504%	$178.9189	$178.92	$178.90	$178.90
Purchase #7	$204.82	11.195%	$227.7496	$227.75	$227.75	$227.70
7 purchase totals =	$806.21		$868.4932	$868.50	$868.50	$868.40