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	$53.52	13.458%	$60.7227	$60.72	$60.70	$60.70
Purchase #2	$33.48	3.241%	$34.5651	$34.57	$34.55	$34.60
Purchase #3	$135.49	5.811%	$143.3633	$143.36	$143.35	$143.40
Purchase #4	$107.40	3.438%	$111.0924	$111.09	$111.10	$111.10
Purchase #5	$49.47	4.633%	$51.7619	$51.76	$51.75	$51.80
Purchase #6	$50.64	12.204%	$56.8201	$56.82	$56.80	$56.80
Purchase #7	$69.35	12.839%	$78.2538	$78.25	$78.25	$78.30
7 purchase totals =	$499.35		$536.5793	$536.57	$536.50	$536.70