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	$142.84	8.667%	$155.2199	$155.22	$155.20	$155.20
Purchase #2	$104.85	6.688%	$111.8624	$111.86	$111.85	$111.90
Purchase #3	$206.89	5.523%	$218.3165	$218.32	$218.30	$218.30
Purchase #4	$46.74	9.287%	$51.0807	$51.08	$51.10	$51.10
Purchase #5	$40.40	13.287%	$45.7679	$45.77	$45.75	$45.80
Purchase #6	$33.27	7.751%	$35.8488	$35.85	$35.85	$35.80
Purchase #7	$168.28	11.644%	$187.8745	$187.87	$187.85	$187.90
7 purchase totals =	$743.27		$805.9707	$805.97	$805.90	$806.00