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	$65.88	9.476%	$72.1228	$72.12	$72.10	$72.10
Purchase #2	$24.26	6.483%	$25.8328	$25.83	$25.85	$25.80
Purchase #3	$77.59	9.119%	$84.6654	$84.67	$84.65	$84.70
Purchase #4	$126.31	10.760%	$139.901	$139.90	$139.90	$139.90
Purchase #5	$92.47	13.286%	$104.7556	$104.76	$104.75	$104.80
Purchase #6	$77.92	3.103%	$80.3379	$80.34	$80.35	$80.30
Purchase #7	$75.98	13.142%	$85.9653	$85.97	$85.95	$86.00
7 purchase totals =	$540.41		$593.5808	$593.59	$593.55	$593.60