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	$69.45	13.481%	$78.8126	$78.81	$78.80	$78.80
Purchase #2	$227.95	5.498%	$240.4827	$240.48	$240.50	$240.50
Purchase #3	$107.55	12.814%	$121.3315	$121.33	$121.35	$121.30
Purchase #4	$59.85	12.557%	$67.3654	$67.37	$67.35	$67.40
Purchase #5	$231.49	4.324%	$241.4996	$241.50	$241.50	$241.50
Purchase #6	$37.80	11.251%	$42.0529	$42.05	$42.05	$42.10
Purchase #7	$115.98	9.583%	$127.0944	$127.09	$127.10	$127.10
7 purchase totals =	$850.07		$918.6391	$918.63	$918.65	$918.70