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	$49.58	3.839%	$51.4834	$51.48	$51.50	$51.50
Purchase #2	$35.51	4.485%	$37.1026	$37.10	$37.10	$37.10
Purchase #3	$186.25	4.397%	$194.4394	$194.44	$194.45	$194.40
Purchase #4	$249.70	5.770%	$264.1077	$264.11	$264.10	$264.10
Purchase #5	$142.28	3.639%	$147.4576	$147.46	$147.45	$147.50
Purchase #6	$12.41	8.507%	$13.4657	$13.47	$13.45	$13.50
Purchase #7	$149.93	5.723%	$158.5105	$158.51	$158.50	$158.50
7 purchase totals =	$825.66		$866.5669	$866.57	$866.55	$866.60