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	$230.39	6.831%	$246.1279	$246.13	$246.15	$246.10
Purchase #2	$43.55	3.663%	$45.1452	$45.15	$45.15	$45.10
Purchase #3	$198.36	12.861%	$223.8711	$223.87	$223.85	$223.90
Purchase #4	$78.93	4.685%	$82.6279	$82.63	$82.65	$82.60
Purchase #5	$127.37	4.119%	$132.6164	$132.62	$132.60	$132.60
Purchase #6	$161.70	5.364%	$170.3736	$170.37	$170.35	$170.40
Purchase #7	$225.62	5.814%	$238.7375	$238.74	$238.75	$238.70
7 purchase totals =	$1,065.92		$1,139.4996	$1,139.51	$1,139.50	$1,139.40