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	$197.91	12.581%	$222.8091	$222.81	$222.80	$222.80
Purchase #2	$139.64	7.615%	$150.2736	$150.27	$150.25	$150.30
Purchase #3	$76.83	11.733%	$85.8445	$85.84	$85.85	$85.80
Purchase #4	$226.40	6.230%	$240.5047	$240.50	$240.50	$240.50
Purchase #5	$124.83	9.354%	$136.5066	$136.51	$136.50	$136.50
Purchase #6	$75.46	12.318%	$84.7552	$84.76	$84.75	$84.80
Purchase #7	$136.98	5.716%	$144.8098	$144.81	$144.80	$144.80
7 purchase totals =	$978.05		$1,065.5035	$1,065.50	$1,065.45	$1,065.50