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	$141.26	6.554%	$150.5182	$150.52	$150.50	$150.50
Purchase #2	$40.30	6.557%	$42.9425	$42.94	$42.95	$42.90
Purchase #3	$141.50	11.544%	$157.8348	$157.83	$157.85	$157.80
Purchase #4	$114.76	11.235%	$127.6533	$127.65	$127.65	$127.70
Purchase #5	$155.39	10.615%	$171.8846	$171.88	$171.90	$171.90
Purchase #6	$230.72	8.172%	$249.5744	$249.57	$249.55	$249.60
Purchase #7	$10.47	12.742%	$11.8041	$11.80	$11.80	$11.80
7 purchase totals =	$834.40		$912.2119	$912.19	$912.20	$912.20