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	$162.67	12.804%	$183.4983	$183.50	$183.50	$183.50
Purchase #2	$118.88	3.758%	$123.3475	$123.35	$123.35	$123.30
Purchase #3	$185.83	4.428%	$194.0586	$194.06	$194.05	$194.10
Purchase #4	$221.45	6.326%	$235.4589	$235.46	$235.45	$235.50
Purchase #5	$5.70	11.862%	$6.3761	$6.38	$6.40	$6.40
Purchase #6	$56.67	5.140%	$59.5828	$59.58	$59.60	$59.60
Purchase #7	$18.50	5.307%	$19.4818	$19.48	$19.50	$19.50
7 purchase totals =	$769.70		$821.8040	$821.81	$821.85	$821.90