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	$236.87	5.175%	$249.128	$249.13	$249.15	$249.10
Purchase #2	$52.59	6.575%	$56.0478	$56.05	$56.05	$56.00
Purchase #3	$173.32	7.116%	$185.6535	$185.65	$185.65	$185.70
Purchase #4	$77.72	9.708%	$85.2651	$85.27	$85.25	$85.30
Purchase #5	$134.50	12.245%	$150.9695	$150.97	$150.95	$151.00
Purchase #6	$136.25	5.789%	$144.1375	$144.14	$144.15	$144.10
Purchase #7	$244.86	10.630%	$270.8886	$270.89	$270.90	$270.90
7 purchase totals =	$1,056.11		$1,142.0900	$1,142.10	$1,142.10	$1,142.10