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	$144.91	6.844%	$154.8276	$154.83	$154.85	$154.80
Purchase #2	$134.52	6.214%	$142.8791	$142.88	$142.90	$142.90
Purchase #3	$84.41	5.214%	$88.8111	$88.81	$88.80	$88.80
Purchase #4	$233.39	6.744%	$249.1298	$249.13	$249.15	$249.10
Purchase #5	$114.79	10.647%	$127.0117	$127.01	$127.00	$127.00
Purchase #6	$199.74	10.485%	$220.6827	$220.68	$220.70	$220.70
Purchase #7	$71.51	8.786%	$77.7929	$77.79	$77.80	$77.80
7 purchase totals =	$983.27		$1,061.1349	$1,061.13	$1,061.20	$1,061.10