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	$50.68	5.634%	$53.5353	$53.54	$53.55	$53.50
Purchase #2	$190.35	12.591%	$214.317	$214.32	$214.30	$214.30
Purchase #3	$230.76	10.614%	$255.2529	$255.25	$255.25	$255.30
Purchase #4	$54.49	9.809%	$59.8349	$59.83	$59.85	$59.80
Purchase #5	$224.54	9.316%	$245.4581	$245.46	$245.45	$245.50
Purchase #6	$140.39	9.745%	$154.071	$154.07	$154.05	$154.10
Purchase #7	$102.79	11.334%	$114.4402	$114.44	$114.45	$114.40
7 purchase totals =	$994.00		$1,096.9094	$1,096.91	$1,096.90	$1,096.90