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	$46.56	13.135%	$52.6757	$52.68	$52.70	$52.70
Purchase #2	$47.39	9.346%	$51.8191	$51.82	$51.80	$51.80
Purchase #3	$118.29	11.311%	$131.6698	$131.67	$131.65	$131.70
Purchase #4	$165.54	3.827%	$171.8752	$171.88	$171.90	$171.90
Purchase #5	$52.92	12.387%	$59.4752	$59.48	$59.50	$59.50
Purchase #6	$102.98	13.624%	$117.01	$117.01	$117.00	$117.00
Purchase #7	$209.50	11.250%	$233.0688	$233.07	$233.05	$233.10
7 purchase totals =	$743.18		$817.5938	$817.61	$817.60	$817.70