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	$19.92	8.347%	$21.5827	$21.58	$21.60	$21.60
Purchase #2	$41.61	4.627%	$43.5353	$43.54	$43.55	$43.50
Purchase #3	$214.32	5.339%	$225.7625	$225.76	$225.75	$225.80
Purchase #4	$135.78	11.407%	$151.2684	$151.27	$151.25	$151.30
Purchase #5	$154.82	4.234%	$161.3751	$161.38	$161.40	$161.40
Purchase #6	$181.94	7.670%	$195.8948	$195.89	$195.90	$195.90
Purchase #7	$72.62	7.804%	$78.2873	$78.29	$78.30	$78.30
7 purchase totals =	$821.01		$877.7061	$877.71	$877.75	$877.80