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	$48.27	13.109%	$54.5977	$54.60	$54.60	$54.60
Purchase #2	$79.83	3.664%	$82.755	$82.76	$82.75	$82.80
Purchase #3	$47.46	7.466%	$51.0034	$51.00	$51.00	$51.00
Purchase #4	$105.75	13.536%	$120.0643	$120.06	$120.05	$120.10
Purchase #5	$146.64	12.493%	$164.9597	$164.96	$164.95	$165.00
Purchase #6	$232.83	6.330%	$247.5681	$247.57	$247.55	$247.60
Purchase #7	$167.48	4.724%	$175.3918	$175.39	$175.40	$175.40
7 purchase totals =	$828.26		$896.3400	$896.34	$896.30	$896.50