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	$227.67	4.610%	$238.1656	$238.17	$238.15	$238.20
Purchase #2	$33.33	4.800%	$34.9298	$34.93	$34.95	$34.90
Purchase #3	$132.55	6.829%	$141.6018	$141.60	$141.60	$141.60
Purchase #4	$242.86	10.868%	$269.254	$269.25	$269.25	$269.30
Purchase #5	$11.91	13.706%	$13.5424	$13.54	$13.55	$13.50
Purchase #6	$71.64	8.382%	$77.6449	$77.64	$77.65	$77.60
Purchase #7	$75.36	6.653%	$80.3737	$80.37	$80.35	$80.40
7 purchase totals =	$795.32		$855.5122	$855.50	$855.50	$855.50