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	$116.58	12.132%	$130.7235	$130.72	$130.70	$130.70
Purchase #2	$169.91	6.857%	$181.5607	$181.56	$181.55	$181.60
Purchase #3	$87.99	10.604%	$97.3205	$97.32	$97.30	$97.30
Purchase #4	$40.98	10.137%	$45.1341	$45.13	$45.15	$45.10
Purchase #5	$237.96	5.190%	$250.3101	$250.31	$250.30	$250.30
Purchase #6	$77.46	6.667%	$82.6243	$82.62	$82.60	$82.60
Purchase #7	$133.91	6.357%	$142.4227	$142.42	$142.40	$142.40
7 purchase totals =	$864.79		$930.0959	$930.08	$930.00	$930.00