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	$150.37	10.462%	$166.1017	$166.10	$166.10	$166.10
Purchase #2	$215.88	3.681%	$223.8265	$223.83	$223.85	$223.80
Purchase #3	$199.82	5.534%	$210.878	$210.88	$210.90	$210.90
Purchase #4	$42.60	4.606%	$44.5622	$44.56	$44.55	$44.60
Purchase #5	$39.80	13.344%	$45.1109	$45.11	$45.10	$45.10
Purchase #6	$176.26	4.637%	$184.4332	$184.43	$184.45	$184.40
Purchase #7	$196.37	9.363%	$214.7561	$214.76	$214.75	$214.80
7 purchase totals =	$1,021.10		$1,089.6686	$1,089.67	$1,089.70	$1,089.70