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	$166.74	13.596%	$189.41	$189.41	$189.40	$189.40
Purchase #2	$226.46	4.584%	$236.8409	$236.84	$236.85	$236.80
Purchase #3	$102.59	12.149%	$115.0537	$115.05	$115.05	$115.10
Purchase #4	$13.64	13.321%	$15.457	$15.46	$15.45	$15.50
Purchase #5	$42.88	13.705%	$48.7567	$48.76	$48.75	$48.80
Purchase #6	$142.89	5.529%	$150.7904	$150.79	$150.80	$150.80
Purchase #7	$80.27	11.619%	$89.5966	$89.60	$89.60	$89.60
7 purchase totals =	$775.47		$845.9053	$845.91	$845.90	$846.00