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	$31.88	10.795%	$35.3214	$35.32	$35.30	$35.30
Purchase #2	$92.80	10.205%	$102.2702	$102.27	$102.25	$102.30
Purchase #3	$225.76	3.706%	$234.1267	$234.13	$234.15	$234.10
Purchase #4	$120.51	5.857%	$127.5683	$127.57	$127.55	$127.60
Purchase #5	$106.67	12.602%	$120.1126	$120.11	$120.10	$120.10
Purchase #6	$91.53	13.330%	$103.7309	$103.73	$103.75	$103.70
Purchase #7	$95.55	8.462%	$103.6354	$103.64	$103.65	$103.60
7 purchase totals =	$764.70		$826.7655	$826.77	$826.75	$826.70