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	$54.80	3.783%	$56.8731	$56.87	$56.85	$56.90
Purchase #2	$149.65	3.187%	$154.4193	$154.42	$154.40	$154.40
Purchase #3	$249.45	6.808%	$266.4326	$266.43	$266.45	$266.40
Purchase #4	$39.50	7.847%	$42.5996	$42.60	$42.60	$42.60
Purchase #5	$245.36	5.126%	$257.9372	$257.94	$257.95	$257.90
Purchase #6	$243.48	10.267%	$268.4781	$268.48	$268.50	$268.50
Purchase #7	$84.25	6.316%	$89.5712	$89.57	$89.55	$89.60
7 purchase totals =	$1,066.49		$1,136.3111	$1,136.31	$1,136.30	$1,136.30