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	$54.30	3.843%	$56.3867	$56.39	$56.40	$56.40
Purchase #2	$48.98	11.178%	$54.455	$54.46	$54.45	$54.50
Purchase #3	$105.55	6.838%	$112.7675	$112.77	$112.75	$112.80
Purchase #4	$195.89	8.310%	$212.1685	$212.17	$212.15	$212.20
Purchase #5	$115.71	10.505%	$127.8653	$127.87	$127.85	$127.90
Purchase #6	$74.71	3.323%	$77.1926	$77.19	$77.20	$77.20
Purchase #7	$150.55	13.822%	$171.359	$171.36	$171.35	$171.40
7 purchase totals =	$745.69		$812.1946	$812.21	$812.15	$812.40