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	$75.51	4.362%	$78.8037	$78.80	$78.80	$78.80
Purchase #2	$74.90	10.327%	$82.6349	$82.63	$82.65	$82.60
Purchase #3	$122.91	3.696%	$127.4528	$127.45	$127.45	$127.50
Purchase #4	$171.75	5.858%	$181.8111	$181.81	$181.80	$181.80
Purchase #5	$49.67	11.146%	$55.2062	$55.21	$55.20	$55.20
Purchase #6	$38.93	3.623%	$40.3404	$40.34	$40.35	$40.30
Purchase #7	$27.55	4.560%	$28.8063	$28.81	$28.80	$28.80
7 purchase totals =	$561.22		$595.0554	$595.05	$595.05	$595.00